Pre-crack your screen. They cannot pawn/sell any device with any sort of crack. It is also a great security feature. As each crack is distinct, nobody will ever be able to swap out your phone without you noticing.

I read of one person a while back who dissuaded a mugger by saying that they worked for the NSA, that their phone would be tracked and therefore would be dangerous to take. It is something to think about. Put a "property of US government" sticker on your phone.