Police are known to use a number of tricks to hide radar from unsuspecting motorists. Some police dress up like road maintenance workers and sometimes even have real road maintenance vehicles to add to the deception when running radar. Surveyor uniforms along with surveyor equipment are also used. Hiding in what appears to be a disabled truck also works well.
However the most original disguise has to be the police officer in Charles Town, West Virginia who hid in a portable toilet (with the door open to view potential speeders) across from the police station running a portable radar. I wonder if he was standing or sitting?
Most portable toilets have walls made from fiberglass, the same material used for aircraft radar radomes (nose cones). Fiberglass is strong and relatively transparent to microwaves. A police officer could blindly aim a radar beam through the fiberglass wall and get a speed reading on passing vehicles.