These are the most common types of tracks for sound design:
The Dialogue (DX),
Automated Dialogue Replacement (ADR),
Foley (FLY),
Sound Effects (SFX),
Ambience (AMB),
Music (MX),
Room Tone (RT)
Instead of trying to come up with some icons which may not fit everyone's taste, I've used the acronyms as icons(mock-up):

I don't have time to learn to build Audacity in order to submit this as a proper patch, so I hope it is okay I share the icons this way?
The icons are saved as xpm and png and are completely free to use:
https://blenderartists.org/uploads/shor ... cNLHNM.zip
The font used is Cinematografica: https://www.dafont.com/cinematografica.font