I hate to put the ALL CAPS RED thing in here, but I feel this is important.
If you clear the ALTSYMBOL character using the game interface (simply delete it), it will crash the game if the currently selected user (pilot) is selected in the all.ini file.
Using the INTERFACE, I cleared the symbol to be null (I don't like it, and figured deleting it would work).
THIS WILL CRASH THE GAME (IT WON'T START). The following is a completely legit icons file generated by the game by simply pressing "DELETE" to clear the symbol.
Code:
mp_dotrange FRIENDLY DOT 25.000002 COLOR 1.6500001 RANGE 0.05 TYPE 1.6500001 ID 0.010000001 NAME 0.020000001 ALTICON 0.1 ALTSYMBOL ALTCOLOR 0
mp_dotrange FOE DOT 25.000002 COLOR 1.6500001 RANGE 0.05 TYPE 1.6500001 ID 0.010000001 NAME 0.020000001 ALTICON 20.0 ALTSYMBOL ALTCOLOR 0