That's actually clever as hell. I leave them on because usually a cop only gets a glance at that part of your window, so I'd rather them see that there are stickers and go on about his or her day. Also, unfortunately, the verbiage in my lease agreement states that my car needs to have up-to-date stickers or they can remove the vehicles. You are right it is a lazy way of keeping inoperable cars out of the complex.