Heat Margin shows you where you've been editing your code!
Download it here: https://visualstudiogallery.msdn.microsoft.com/66a4194a-4271-493f-8d87-91052d7db09d
Visual studio has a feature built in to that shows you where you've edited your file (green for saved, yellow for unsaved). But over time, your entire document will show the green bar!
With heat Margin as you edit lines, indicators are added in the scroll bar and next to the line numbers (much like the default green and yellow makers you're used to).
The differnce with Heat Margin is as you edit more lines, previouly edited line indicators start to fade. You'll quickly start to build up an idea of where you are working!
Works with 2015, 2017 and 2019.
With special thanks to https://github.com/laurentkempe/GitDiffMargin for getting me quickly up to speed with VS extensions!
If for some reason you cannot get it to launch with the debugger attached, try going to Project Settings -> Debug and setting Start external program to "C:\Program Files (x86)\Microsoft Visual Studio 12.0\Common7\IDE\devenv.exe" (or whereever your VS is) and command line arguments to "/rootSuffix Exp".