If it was stolen, and the former owner called up Apple, then Apple has it in their database. When my Powerbook was stolen I called Applecare and got a refund for the remainder of my time left on the Applecare plan and then if someone ever takes that pbook in for service, they know it's stolen. I don't know if you can do much else. Maybe google its serial number and see if anyone has ever posted that number on a forum because they had their computer stolen?