I was under the impression that any form of vehicle or person using speed measuring equipment had to be easily identifiable.
Otherwise they may as well paint those gigantic yellow boxes a different colour to blend in with the environment. Heck they may as well take it a step further and start hiding them behind signs and trees.
This is not true, according to the speed awareness course I went on.
Cameras/traps are highlighted "for your benefit" because the goal is "safety, not revenue".
Take from that what you will.