The style name is PrintUsage. It is defined in the stylesheet notebook Core.nb which you can find in the directory:
$InstallationDirectory\SystemFiles\FrontEnd\StyleSheets
It has the following settings:
CellFrame -> {{0, 0}, {0, 3}}
CellFrameColor -> RGBColor[1, 0.6000000000000001, 0]
Background -> RGBColor[1, 0.993332, 0.899718]
You can use the OptionInspector to set DefaultNewCellStyle or DefaultReturnCreatedCellStyle to PrintUsage. You can also change these settings at the notebook, front-end session or front-end level using
SetOptions[xx,DefaultNewCellStyle->"PrintUsage"]
where xx is EvaluationNotebook[] or $FrontEndSession, or $DefaultFrontEnd.
A third alternative is to use the right-click context menu on a cell bracket,choose Style->Other and type PrintUsage in the dialog box to change the style of that cell.
One important issue with the above approach is that a cell with PrintUsage style is not editable. So, you may want to define your custom style using something like
this answer by Mike Honeychurch:
SetOptions[EvaluationNotebook[],
StyleDefinitions ->
Notebook[{Cell[StyleData[StyleDefinitions -> "Default.nb"]],
Cell[StyleData["myPrintUsageStyle"], Editable -> True, Evaluatable -> True,
CellFrame -> {{0, 0}, {0, 3}}, CellMargins -> {{66, 10}, {10, 5}},
CellFrameColor -> RGBColor[1, 0.6000000000000001, 0],
Background -> RGBColor[1, 0.993332, 0.899718]]},
Saveable -> True, StyleDefinitions -> "PrivateStylesheetFormatting.nb"]];
and use it in place of PrintUsage using any of the usage options mentioned above, e.g.,
SetOptions[EvaluationNotebook[], DefaultNewCellStyle -> "myPrintUsageStyle"]
tutorial/EnteringTwoDimensionalInputin the Mathematica Documentation? – Peter Breitfeld Apr 27 '12 at 12:43