At my bicycle co-op, we were discussing the best ways to steal a bike to determine the best ways to combat the methods. We even went so far as suggesting special chemical coats on U-locks to incapacitate a would-be thief with a battery powered angle grinder. But when I was told about this one particular scheme, I freaked out a bit:
What thieves are doing at college campuses, parking structures, offices, and other places with bike racks and security guards/bike police is using the men/women who are presumably keeping your bikes safe to walk away with your bike, without lifting a finger to cut your lock!
A thief arrives at the chosen bike, brings his OWN lock, locks it on YOUR bike, then goes to the security/campus police asking for assistance in the removal of your lock, saying that some "vandal" thought it'd be funny to lock their lock on their bike. With your lock removed by the guard/cops, the thief rides away with your $1000+ investment.
Sure, the upside is that the guard or cops get a good look at the thief, but if they never show up to that campus again, what good does it do? Also, if they're caught in the act (you get out of class/work early and check on your bike), they get a slap on the wrist because he gets off saying it was a prank!
My advice would be to let your security/campus police know about this new method and suggest some sort of on-campus bike registration.