Police arrested a notorious Toronto bike thief a few years back, and I persuaded my biking buddy to drive me over to the open house where they were showing some of the 2,000 bikes they recovered -- our bikes had been stolen a few weeks before the arrest when we stupidly locked them in a quietish downtown spot with a flimsy lock. We found the bikes, only to discover that my bike store receipt had the serial number off by one. Police looked at us, the bikes and the cellphone picture I showed them of the two of us riding somewhere in Vermont and handed both bikes back. Business card idea would have made it all a lot simpler.