From my experience, most thieves are people you know. A good deterrent for receivers is to show people that you're taking the faceplate out of the car instead of hiding it in the center console or glove compartment. They might be kind of big, but it's better to have it in your pocket (or purse for the ladies) than have it in a theives hands.
Most of us have done it in the past, taken the faceplate off when we first get the receiver installed, then we get lazy and start to leave it on, or take it off and put it under the seat, in the glove compartment, sun visor (kind of stupid but I've seen it done), center console, or (the absolute worst) in the front seat. Alot of the would-be theives are the ones you know that may be deadbeats or have fallen on bad times and claim to be cool with you but are only trying to rip you and others off.