Here it is deinitley ilegal to drive/ride anything without a plate (or temporary permit if you just bought it new). Not sure what the fine/punishment is, but I am pretty sure it is something harsh. I have not noticed any bikes out here running around with plates.
I do remember about a year ago there was an underground ring that was selling fake IDs, SSNs, passports, green cards and etc was also selling stolen licence plates.
Soren
