C'mon man. If you're claiming you can't verify the numbers on a locked bike then you're not trying hard enough. If I seriously suspected a bike locked to a rack was mine, I'd get the number off the bottom bracket, even if I had to lay in the mud to do it. Hell, holding your phone under the bike for a quick pic should do it.
Get the number -- no excuses. If it's yours, slap a big, fat lock on it and call the police. Be ready to prove it's yours when they arrive. Oh, and bring something to cut off the other guys lock. I recommend an 18v cutting wheel.
-Kedosto