I use the NCE 10amp wireless command set to run my MTH PS-3 locomotives. I have not remapped my buttons, yet. So point I do plan to after I've upgraded a couple more of my conventional locomotives to DCC.
But F3 is engine startup/shut down out of the box for PS-3. A short horn is F24. So to use it I have to push my option key twice to get to F20-F29 and then I push the 4 key. As it's a toggle I have to do this twice for every time I want to play the short horn, which is a pain, so it'll be remapped to a single digit. It'll probably become F4 as I never use station/freight announcements.