By the way, when this happened to my friends car, the police 60 miles way who found it had no idea who's car it was. He had a sticker on it with a friends business name and phone number. They called him. The moral of the story is have a sticker on your car with a phone number on it.
That is a good reason to keep one tagged with a plate on it. It is worth the $25 a year(your price may vary) to keep that in the DMV Database for tracking purposes in the event it is stolen.