I drop one of my business cards down the seat post.

20 years ago a guy stole my bike and I ran him down and the police came. The guy keep saying it was his bike and just going on about wanting me arrested for knocking down. I let him go on then asked if he had ever seen me before and where he got the bike, after he said he had never seen me before I asked the cop to watch him close while his partner looked in the seat post.
You know the rest of the story!