32 point SOHC Bold Serif? Not to be confused with 550 Nighthawk Bold Italic. Be advised that the blue 550F used a different color drop shadow than either of the oranges, and after 75 the tank decals were a dot-matrix as opposed to halftones.
Haha. Just kidding and talking out of my butt trumpet. I'm also curious to hear a serious answer to this question, as well as the font of the 550 tank badges. My 550F isn't badged as a Honda, and I'd like to keep perpetuating the mystery.