I just write in the numbers (0, 1-3, 4-7), lightly in pencil on paper, on my tablet (using the app MobileSheets) with the stylus. On the tablet, of course, you can erase or redo these notes at any time.
But I also rely on some other short hand of sorts. For example, on my treble flute I usually play the lower E flat with four fingers (double fork), but sometimes I want a softer sound, so I’ll simply write “3f” or “2f” above the E flat, which tells me how many fingers I want to use for it.
For other notes I have regular alternate fingerings, for example for the middle G (on my subbass), I have three fingerings I use, “G1” (standard), “G2” (second thumb key added) and “G3” (played in the same register as A, i.e. both hands). Of course, these are really only meaningful to me.