Based on Oleksandr's excellent [design idea][1] here is my re-implementation of his package which offers much richer set of shapes.


----------


## How to install the package ##

The most recent version of the package can be installed from GitHub by evaluating the following:

    (* Load the package code *)
    package = 
      Import["http://raw.github.com/AlexeyPopkov/PolygonPlotMarkers/master/PolygonPlotMarkers.m", "Text"];

    (* Install the package (existing file will be overwritten!) *)
    Export[FileNameJoin[{$UserBaseDirectory, "Applications", 
        "PolygonPlotMarkers.m"}], package, "Text"];

For manual installation copy the code from the bottom of this post and save as "PolygonPlotMarkers.m" in the directory `SystemOpen[FileNameJoin[{$UserBaseDirectory, "Applications"}]]`.


----------
## Description of the package ##

>  - The basic usage syntax is <code>PolygonMarker[*shape*, *size*]</code> where <code>*shape*</code> is a name of built-in shape or a list of 2D coordinates describing a non-selfintersecting polygon. The <code>*size*</code> can be given as a number or in `Scaled` or `Offset` form. 

>  - `PolygonMarker[All]` and `PolygonMarker[]` return the list of names of built-in shapes. 

>  - <code>PolygonMarker[*shape*, *size*]</code> returns `Polygon` graphics primitive which can be used in `Graphics`.

>  - With `Offset` <code>*size*</code> specification the plot marker has fixed size specified in *printer's points* independent of the size of the plot. 

>  - `PolygonMarker`s with identical <code>*size*</code> specifications have equal areas (not counting the area taken by the **edge** of generated `Polygon`). <code>PolygonMarker[*shape*, *size*]</code> returns shape with area <code>*size*<sup>2</sup></code> in the internal coordinate system of `Graphics`. <code>PolygonMarker[*shape*, Offset\[*size*\]]</code> returns shape with area <code>*size*<sup>2</sup></code> *square printer's points*.

>  - The centroid of polygon returned by <code>PolygonMarker[*shape*, *size*]</code> is always placed at `{0, 0}` in the internal coordinate system of `Graphics`.

>  - <code>PolygonMarker[*shape*, *size*, *positions*]</code> where <code>*positions*</code> is a list of 2D coordinates evaluates to <code>Translate[PolygonMarker[*shape*, *size*], *positions*]</code>. It represents a collection of multiple identical copies of the shape with centroids placed at <code>*positions*</code>.

----------


## Basic examples of use ##

The complete list of built-in named shapes:

    Needs["PolygonPlotMarkers`"]

    allShapes = PolygonMarker[All]
    Tooltip[Graphics[{FaceForm[Hue@Random[]], 
         EdgeForm[{Black, Thickness[0.003], JoinForm["Miter"]}], PolygonMarker[#, 1]}, 
        ImageSize -> 30, PlotRange -> 1.5, PlotRangePadding -> 0, 
        ImagePadding -> 0], #] & /@ allShapes

>     {"TripleCross", "Y", "UpTriangle", "UpTriangleTruncated", "DownTriangle", 
>     "DownTriangleTruncated", "LeftTriangle", "LeftTriangleTruncated", "RightTriangle", 
>     "RightTriangleTruncated", "ThreePointedStar", "Cross", "DiagonalCross", "Diamond", 
>     "Square", "FourPointedStar", "DiagonalFourPointedStar", "FivefoldCross", "Pentagon", 
>     "FivePointedStar", "FivePointedStarThick", "SixfoldCross", "Hexagon", "SixPointedStar", 
>     "SixPointedStarSlim", "SevenfoldCross", "SevenPointedStar", "SevenPointedStarNeat", 
>     "SevenPointedStarSlim", "EightfoldCross", "Disk", "H", "I", "N", "Z", "S", "Sw", "Sl"}

[![all available shapes][2]][2]

When used in conjunction with such functions as `ListPlot`, `ListLinePlot`, `ListLogPlot` etc. it is highly recommended to include **`AlignmentPoint -> {0, 0}`** option for achieving exact positioning of markers on the plot (this option with default `ImagePadding` and `ImageMargins` doesn't affect `Export`ing to PDF, EPS or SVG but [affects][3] on-screen rendering and `Export`ing to raster formats):

    (* full marker which picks up the PlotStyle automatically *)
    fm[name_, size_: 7] := 
     Graphics[{EdgeForm[], PolygonMarker[name, Offset[size]]}, AlignmentPoint -> {0, 0}];

    SeedRandom[25] (* for reproducibility *)
    ListPlot[
     Table[Accumulate@RandomReal[1, 10] + i, {i, 6}],
     PlotMarkers -> 
      fm /@ {"Triangle", "LeftTriangle", "Diamond", "ThreePointedStar", "UpTriangleTruncated",
         "Square"},
     Joined -> True, PlotStyle -> ColorData[54, "ColorList"]]

> [![plot][4]][3]

Automatic plot legends (*Mathematica* 10 or higher) often require larger value for `LegendMarkerSize` option in order to avoid cropping:

    (* empty marker which picks up the PlotStyle automatically,
       see https://mathematica.stackexchange.com/a/158221/280  *)
    em[name_, size_: 7] := 
     Graphics[{Dynamic@
        EdgeForm@Directive[CurrentValue["Color"], JoinForm["Round"], AbsoluteThickness[2], 
          Opacity[1]], FaceForm[White], PolygonMarker[name, Offset[size]]}, 
      AlignmentPoint -> {0, 0}]

    SeedRandom[2]
    ListPlot[
     Table[Accumulate@RandomReal[1, 10] + i, {i, 3}],
     PlotMarkers -> em /@ {"Triangle", "Square", "Diamond"},
     Joined -> True, PlotLegends -> PointLegend[Automatic, LegendMarkerSize -> {40, 25}]
     ]

> [![plot][5]][4]

## Advanced usage ##

The third argument of `PolygonMarker` can be used to specify the coordinate(s) where the shape should be placed:

    Graphics[{FaceForm[], EdgeForm[{Black, AbsoluteThickness[1], JoinForm["Miter"]}],
      PolygonMarker["Circle", Offset[7], RandomReal[{-1, 1}, {20, 2}]],
      PolygonMarker["ThreePointedStar", Offset[7], RandomReal[{-1, 1}, {20, 2}]], 
      PolygonMarker["FourPointedStar", Offset[7], RandomReal[{-1, 1}, {20, 2}]], 
      PolygonMarker["FivePointedStar", Offset[7], RandomReal[{-1, 1}, {20, 2}]]}, 
     AspectRatio -> 1/2]

> [![plot][6]][3]

The package allows to use arbitrary polygon as a plot marker. Here is an auxiliary function which converts simple glyph into a set of points suitable for `PolygonMarker`:

    pts[l_String] := 
      First@Cases[
        ImportString[
         ExportString[Style[l, FontFamily -> "Verdana", FontSize -> 20], 
          "PDF"], "PDF"], c_FilledCurve :> c[[2, 1]], Infinity];

(This conversion is approximate. If precise conversion is needed one can apply one of the methods described in "[How can I adaptively simplify a curved shape?][7]")

An example of use:

    ListPlot[ConstantArray[Range[5], 7] + Range[0, 12, 2], 
     PlotStyle -> Gray, Joined -> True, PlotMarkers -> {
       Graphics[{FaceForm[LightBlue], EdgeForm[Black], 
         PolygonMarker[pts["U"], Scaled[0.05]]}, AlignmentPoint -> {0, 0}],
       Graphics[{FaceForm[LightBlue], EdgeForm[Black], 
         PolygonMarker[pts["S"], Scaled[0.05]]}, AlignmentPoint -> {0, 0}],
       Graphics[{FaceForm[Red], EdgeForm[Black], 
         PolygonMarker["FivePointedStar", Scaled[0.05]]}, AlignmentPoint -> {0, 0}],
       Graphics[{FaceForm[Yellow], EdgeForm[Black], 
         PolygonMarker["FourPointedStar", Scaled[0.05]]}, AlignmentPoint -> {0, 0}],
       Graphics[{FaceForm[Green], EdgeForm[Black], 
         PolygonMarker["DownTriangle", Scaled[0.05]]}, AlignmentPoint -> {0, 0}], 
       Graphics[{FaceForm[Brown], EdgeForm[Black], 
         PolygonMarker["DiagonalSquare", Scaled[0.05]]}, AlignmentPoint -> {0, 0}], 
       Graphics[{FaceForm[Blue], EdgeForm[Black], 
         Disk[{0, 0}, Scaled[0.05/Sqrt[π]]]}, AlignmentPoint -> {0, 0}]},
     PlotRange -> {{0, 6}, {0, 18}}]

> [![plot][8]][7]

Here is an example of a plot where plotting symbols significantly overlap, I use here some of the symbols [recommended][9] by [William Cleveland][10] in his early works:

    SeedRandom[11] (* for reproducibility *)
    ListPlot[RandomReal[{-1, 1}, {6, 20, 2}], PlotMarkers -> {
       Graphics[{FaceForm[None], EdgeForm[{Black, Thickness[.008]}], 
         Disk[{0, 0}, Scaled[0.03/Sqrt[π]]]}, AlignmentPoint -> {0, 0}],
       Graphics[{FaceForm[None], EdgeForm[{Black, Thickness[.008]}], 
         PolygonMarker["UpTriangle", Scaled[0.03]]}, AlignmentPoint -> {0, 0}],
       Graphics[{FaceForm[Black], EdgeForm[None], 
         PolygonMarker["Cross", Scaled[0.03]]}, AlignmentPoint -> {0, 0}],
       Graphics[{FaceForm[Black], EdgeForm[None], 
         PolygonMarker[pts["U"], Scaled[0.03]]}, AlignmentPoint -> {0, 0}],
       Graphics[{FaceForm[Black], EdgeForm[None], 
         PolygonMarker["Sl", Scaled[0.03]]}, AlignmentPoint -> {0, 0}],
       Graphics[{FaceForm[Black], EdgeForm[None], 
         PolygonMarker[pts["W"], Scaled[0.03]]}, AlignmentPoint -> {0, 0}]},
     Frame -> True, Axes -> False, PlotRangePadding -> Scaled[.1]]

> [![plot][11]][10]

Additional examples and explanations can be found in the following answers:

 - [Plot markers where the boundary has the same hue as the body but is darker][15]

 - [Perfect vertical alignment of `PointLegend` markers and their labels][12]

 - [Making antisymmetric curvilinear marker "S"][13]

 - [How to specify `PlotMarkers` that scale when graphic is resized?][14]





----------

----------

The code of the package
-----------------------


    BeginPackage["PolygonPlotMarkers`"];
    
    ClearAll[PolygonMarker];
    PolygonMarker::usage = 
      "\!\(\*RowBox[{\"PolygonMarker\", \"[\", RowBox[{StyleBox[\"shape\", \"TI\"], \",\", \
    StyleBox[\"size\", \"TI\"]}], \"]\"}]\) returns Polygon of \!\(\*StyleBox[\"shape\", \"TI\
    \"]\) with centroid at {0,0} and area \!\(\*SuperscriptBox[StyleBox[\"size\", \"TI\"], \
    StyleBox[\"2\", \"TR\"]]\).";
    SyntaxInformation[PolygonMarker] = {"ArgumentsPattern" -> {_, _., _.}};
    
    Begin["`Private`"];
    
    ClearAll[PolygonArea, PolygonCentroid, LineIntersectionPoint, ngon, nstar, ncross, scale, coords];
    (* The shoelace method for computing the area of polygon
    https://mathematica.stackexchange.com/a/22587/280 *)
    PolygonArea[pts_?MatrixQ] := 
      Abs@Total[Det /@ Partition[pts, 2, 1, 1]]/2;
    (* https://mathematica.stackexchange.com/a/7715/280 *)
    PolygonCentroid[pts_?MatrixQ] := 
      With[{dif = Map[Det, Partition[pts, 2, 1, {1, 1}]]}, 
       ListConvolve[{{1, 1}}, 
          Transpose[pts], {-1, -1}].dif/(3 Total[dif])];
    (* https://mathematica.stackexchange.com/a/51399/280 *)
    LineIntersectionPoint[{a_, b_}, {c_, d_}] := 
      (Det[{a, b}] (c - d) - Det[{c, d}] (a - b))/Det[{a - b, c - d}];
    
    ngon[n_, phase_: 0] := 
      Table[{0, 1}.RotationMatrix[2 k Pi/n + phase], {k, 0, n - 1}];
    (* 
      nn - number of vertices in related polygram
      step - step at which vertices in the polygram are connected
      n - number of points in the final star 

      an illustration: 
      http://en.wikipedia.org/wiki/Star_polygon#Simple_isotoxal_star_polygons
    *)
    nstar[n_ /; n >= 5, phase_: 0] := nstar[n, 2, n, phase];
    nstar[nn_, step_, n_, phase_: 0] /; 
       Divisible[nn, n] && nn/2 > step > nn/n := 
      Module[{a1, a2, b1, b2, ab},
       {a1, a2, b1, b2} = ngon[nn][[{1, 1 + step, 1 + nn/n, nn/n - step}]];
       ab = LineIntersectionPoint[{a1, a2}, {b1, b2}];
       Flatten[
        Table[{a1, ab}.RotationMatrix[2 k Pi/n + phase], {k, 0, n - 1}], 
        1]];
    (* a - semiwidths of the crossing stripes *)
    ncross[n_, phase_: 0, a_: 1/10] := 
      Flatten[NestList[#.RotationMatrix[2 Pi/n] &, {{-a, 1}, {a, 1}, {a, 
           a Cot[Pi/n]}}.RotationMatrix[phase], n - 1], 1];
    
    (* Unitizes the area of the polygon *)
    scale[coords_] := Chop[#/Sqrt@PolygonArea@#] &@N[coords, {18, 18}];

    coords["UpTriangle" | "Triangle"] = ngon[3] // scale;
    coords["DownTriangle"] = ngon[3, Pi/3] // scale;
    coords["LeftTriangle"] = ngon[3, Pi/6] // scale;
    coords["RightTriangle"] = ngon[3, -Pi/6] // scale;
    coords["ThreePointedStar"] = nstar[12, 5, 3] // scale;
    coords["DiagonalSquare" | "Diamond"] = ngon[4, 0] // scale;
    coords["Square"] = ngon[4, Pi/4] // scale;
    coords["FourPointedStar"] = nstar[8, 3, 4] // scale;
    coords["DiagonalFourPointedStar"] = nstar[8, 3, 4, Pi/4] // scale;
    coords["Pentagon"] = ngon[5] // scale;
    coords["FivePointedStar"] = nstar[5] // scale;
    coords["FivePointedStarThick"] = nstar[20, 7, 5] // scale;
    coords["Hexagon"] = ngon[6] // scale;
    coords["SixPointedStar"] = nstar[6] // scale;
    coords["SixPointedStarSlim"] = nstar[12, 5, 6] // scale;
    coords["SevenPointedStar"] = nstar[7] // scale;
    coords["SevenPointedStarNeat"] = nstar[14, 5, 7] // scale;
    coords["SevenPointedStarSlim"] = nstar[14, 6, 7] // scale;
    coords["Cross" | "+"] = ncross[4] // scale;
    coords["DiagonalCross" | "X" | "x"] = ncross[4, Pi/4] // scale;
    coords["TripleCross" | "TripleCrossUp"] = ncross[3] // scale;
    coords["TripleCrossDown" | "Y" | "y"] = ncross[3, Pi/3] // scale;
    coords["FivefoldCross"] = ncross[5] // scale;
    coords["SixfoldCross"] = ncross[6] // scale;
    coords["SevenfoldCross"] = ncross[7] // scale;
    coords["EightfoldCross"] = ncross[8] // scale;

    (* The truncated triangle shape originates from the Cross's Theorem
    http://demonstrations.wolfram.com/CrosssTheorem/  *)
    coords["UpTriangleTruncated" | "TriangleTruncated" | "TruncatedTriangle"] = 
      Flatten[{{-3, 6 + Sqrt[3]}, {3, 6 + Sqrt[3]}}.RotationMatrix[# Pi/3] & /@ 
        {0, 2, 4}, 1] // scale;
    coords["DownTriangleTruncated"] = 
      coords["UpTriangleTruncated"].ReflectionMatrix[{0, 1}];
    coords["LeftTriangleTruncated"] = 
      coords["UpTriangleTruncated"].RotationMatrix[Pi/6];
    coords["RightTriangleTruncated"] = 
      coords["UpTriangleTruncated"].RotationMatrix[-Pi/6];
    (* Circle approximated by 24-gon *)
    coords["Circle" | "Disk"] = ngon[24] // scale;

    (* Plotting symbols recommended in [Cleveland W.S. The Elements of Graphing Data (1985)] *)
    (* Symmetric symbol "H" *)
    coords["H"] = 
      Join[#, -#] &@Join[#, Reverse@#.{{1, 0}, {0, -1}}] &@{{333, 108}, {333, 630}, {585, 630}} // scale;
    (* Symmetric symbol "I" *)
    coords["I"] = 
      Join[#, -#] &@{{-20, -68}, {-64, -68}, {-64, -104}, {64, -104}, {64, -68}, {20, -68}} // scale;
    (* Antisymmetric symbol "N" *)
    coords["N"] = Join[#, -#] &@{{18, -32}, {30, -32}, {30, 32}, {17, 32}, {17, -12}} // scale;
    (* Antisymmetric symbol "Z" *)
    coords["Z"] = Join[#, -#] &@{{-567, -432}, {-567, -630}, {567, -630}, {567, -414}, {-234, -414}} // scale;
    (* Antisymmetric symbol "S" (simple) *)
    coords["S"] = 
      Join[#, -#] &@{{-176, -54}, {116, -54}, {167, -100}, {167, -170}, {116, -216}, {-284, -216}, 
                     {-284, -324}, {176, -324}, {293, -216}, {293, -54}} // scale;
    (* Antisymmetric symbol "S" (curved, long) *)
    coords["LongS"|"SLong"|"Sl"] = Join[#, -#] &@ {{-49/16, -3/11}, {-425/91, 23/28}, {-141/26, 31/12}, 
      {-165/32, 88/19}, {-167/45, 106/17}, {-24/17, 149/21}, {121/69, 233/33}, {130/27, 31/5}, 
      {130/27, 118/29}, {127/47, 199/39}, {7/20, 233/42}, {-12/7, 139/26}, {-65/21, 139/31}, 
      {-395/113, 114/35}, {-157/52, 77/39}, {-83/44, 56/41}, {9/22, 39/43}} // scale;
    (* Antisymmetric symbol "S" curved, wide *)
    coords["WideS" | "SWide" | "Sw"] = 
      Join[#, -#] &@{{80/11, -3/5}, {49/6, -9/4}, {97/12, -41/11}, {39/5, -35/8}, {88/13, -65/12}, 
          {51/10, -49/8}, {2, -13/2}, {-20/11, -13/2}, {-37/8, -81/13}, {-81/13, - 40/7}, 
          {-59/8, -54/11}, {-81/10, -26/7}, {-70/11, -29/9}, {-57/11, -46/11}, {-11/4, -33/7}, 
          {11/7, -19/4}, {16/3, -37/9}, {31/5, -38/11}, {32/5, -38/13}, {37/6, -49/24}, {61/13, -6/5}, 
          {23/7, -13/14}, {-25/9, -4/5}, {-23/4, -3/13}} // scale;
    
    PolygonMarker[name_String, size_?NumericQ] := 
      Polygon[size coords[name]];
    PolygonMarker[name_String, (h : Scaled | Offset)[size_?NumericQ]] := 
      Polygon[h[size #, {0, 0}] & /@ coords[name]];
    PolygonMarker[coords : {{_?NumericQ, _?NumericQ} ..}, 
       size_?NumericQ] := 
      Polygon[size N[
         scale[Transpose[
           Transpose[coords] - PolygonCentroid[coords]]], {16, 16}]];
    PolygonMarker[coords : {{_?NumericQ, _?NumericQ} ..}, 
       Scaled[size_?NumericQ]] := 
      Polygon[Scaled[size #, {0, 0}] & /@ 
        N[scale[Transpose[
           Transpose[coords] - PolygonCentroid[coords]]], {16, 16}]];
    PolygonMarker[arg : _String | {{_?NumericQ, _?NumericQ} ..}, 
       size : _?NumericQ | (Scaled | Offset)[_?NumericQ], 
       positions : {_?NumericQ, _?NumericQ} | {{_?NumericQ, _?NumericQ} ..}] := 
      Translate[PolygonMarker[arg, size], positions];
    (* The list of all available shapes *)
    PolygonMarker[] = 
     PolygonMarker[All] = {"TripleCross", "Y", "UpTriangle", 
       "UpTriangleTruncated", "DownTriangle", "DownTriangleTruncated", 
       "LeftTriangle", "LeftTriangleTruncated", "RightTriangle", 
       "RightTriangleTruncated", "ThreePointedStar", "Cross", 
       "DiagonalCross", "Diamond", "Square", "FourPointedStar", "DiagonalFourPointedStar",
       "FivefoldCross", "Pentagon", "FivePointedStar", 
       "FivePointedStarThick", "SixfoldCross", "Hexagon", 
       "SixPointedStar", "SixPointedStarSlim", "SevenfoldCross", 
       "SevenPointedStar", "SevenPointedStarNeat", "SevenPointedStarSlim",
        "EightfoldCross", "Disk", "H", "I", "N", "Z", "S", "Sw", "Sl"};
    (* A subset of plot markers suitable for use when plotting symbols on the plot 
    significantly overlap. *)
    PolygonMarker["Overlap"] = {"TripleCross", "Y", "UpTriangle", "DownTriangle", 
       "LeftTriangle", "RightTriangle", "ThreePointedStar", "Cross", "DiagonalCross", 
       "Diamond", "Square", "FourPointedStar", "DiagonalFourPointedStar", "FivefoldCross", 
       "FivePointedStar", "FivePointedStarThick", "Disk", "H", "I", "N", "Z", "S", "Sl"};
    
    End[];
    
    EndPackage[];


  [1]: https://mathematica.stackexchange.com/a/84858/280
  [2]: https://i.sstatic.net/r7g9I.png
  [3]: https://mathematica.stackexchange.com/q/137884/280
  [4]: https://i.sstatic.net/1KKlH.png
  [5]: https://i.sstatic.net/nZXgt.png
  [6]: https://i.sstatic.net/QGBjB.png
  [7]: https://mathematica.stackexchange.com/q/137937/280
  [8]: https://i.sstatic.net/eZ6a2.png
  [9]: https://graphicdesign.stackexchange.com/q/36908/946
  [10]: http://www.stat.purdue.edu/~wsc/
  [11]: https://i.sstatic.net/pH9P8.png
  [12]: https://mathematica.stackexchange.com/a/137758/280
  [13]: https://mathematica.stackexchange.com/a/138348/280
  [14]: https://mathematica.stackexchange.com/a/145891/280
  [15]: https://mathematica.stackexchange.com/a/158221/280