How to add a "Running" indicator to title bar in Slideshow presentation mode?

Question

When in presentation mode a Slideshow notebook's cells are hidden. This is good to have when presenting. However, if you have some cells in your presentation that take more than a few seconds to execute it would be useful to have some indicator in title bar that shows when a cell is running. This would be particularly useful in full-screen mode.

I am thinking of having the same little orange disk that appears on the Mathematica icon when it is running to appear in the right-hand side of title bar of the presentation when it is running a cell.

I know exceptionally little about front-end tokens/programming. I believe I need to use EvaluationNotebook and somehow with SetOptions place a Dynamic in the title bar that checks some built-in variable to see if the notebook is executing. I had a look withNames["$*"]` but nothing jumped out as being the current one to use.

I found WindowTitle.

SetOptions[EvaluationNotebook[], WindowTitle -> "test"]

But it seems to only take strings as the following inserts $Failed into the window title.

SetOptions[EvaluationNotebook[], WindowTitle -> Graphics[Disk[]]]

There appears to be a way to do this because there is a menu drop-down in the title bar when in presentation mode.

Any ideas?

Answer 1

So I have some more complex ideas in mind but this is quite nice and short:

SetOptions[EvaluationNotebook[], {
  CellProlog :> SetOptions[EvaluationCell[], ShowCellBracket -> True],
  CellEpilog :> SetOptions[EvaluationCell[], ShowCellBracket -> Inherited]
  }
]

So it will show bracket when you evaluate cell and switch it back when it is over.