I believe the story is something like pontiac pegasus was an early possible name for the car and the ornament was designed early on and after the naming "contest" where they picked fiero it was too late to change it. I believe i read both names were trademarked well before production so the fiero name being selected as part of a contest is probably bunk.
Got to be honest the first time I owned one I never knew what the symbol was supposed to be, it's pretty stylized and small. Only this time around with all the internet resources did I finally figure it out.