You have probably all seen or heard about the license plate covers which are supposed to shield your plate number from being photographed by speed and red light cameras. It appears that some police vehicles are equipt with such plate covers, including one FPS(Federal Protective Services, a component of the Department of Homeland Security) vehicle which was photographed in Montgomery County Maryland.
(1) Cover any of the characters of a vehicle’s registration plate; or
(2) Distort a recorded image of any of the characters of a vehicle’s registration plate recorded by a traffic control signal monitoring system under § 21-202.1 of this article."
and having one on your plate carries a $60 fine. In Virginia, the devices could run you up to a $200 fine, and in DC the maximum fine would be a whopping $500.
In 2005 WTOP reported how some local DC police vehicles had been found with the plate covers, and police responded that they would inform the officers to remove the covers from their plates. In fact in DC city officials have gone so far as to claim even a license plate frame is illegal if it covers the "Taxation Without Representation" slogan on the plates.
Of course the DHS does not run speed or red light cameras the way local police in Maryland and DC do. They only have mobile vans which can look inside your car and covertly scan people in crowds.