here is the thing. if you get stopped by the police, i don't think they can tell. but if you get in a major accident with a possible hefty lawsuit, as seen here, you can be sure the other party is going to do everything they can to find out the legality of your ride. and, if it is technically illegal then i don't know how that will go in the courts even if you were not technically at fault or if it comes down to a "he said, she said" argument.
also, i like 4 stroke for simplicity and little maintenance.