An old couch or mattress left in an alley or vacant lot. These things attract bums like flies. The cops know that they can usually find bums there arrest them for warrants, vagrancy etc
Todd: Can you help me move my old couch into the alley for the trash truck to pick it up?
Charlie: You don't want to lay out bum bait do you? You'll have some hobo or junkie sleeping on it by the morning.