RE: The official Super Smash Brawl thread/characters.
No, it probably means that you can't have more than one motorcycle per Wario character on the screen at a time. My guess is that, since that one picture shows Mario hauling the motorcycle away, others can chuck it off the arena if left unguarded. That would be a severe handicap for Wario if he couldn't use the move for the rest of the match, so he can probably conjure another one, but once it's on the screen, you have to get on it in order to use that special attack again.