[ARCHIVE ANSWER]

Don't mix up undercover and unmarked vehicles. Unmarked vehicles are simple to spot with their internal light
bars, push bumpers, and antennas. License plates marked "EXEMPT" is a clear giveaway that the vehicle is part of some "government" fleet. Vehicle details such as pristine maintenance and type of tires may help determine its purpose.An undercover car is just an ordinary car. It could be a rental car or truck, a previously impounded vehicle, a taxi cab, or a personal vehicle of one of the kops, which is unlikely. They will also rotate vehicles every six months to a year and sell off their old ones and get different ones, so as to avoid being burned. Very few of them will have lights or radios. Most of them will have no equipment at all. That is the best way to do surveillance. If they need a car pulled over they can simply use their handheld radio or their phone and call in a marked patrol unit to do it for
them.
The question you should ask yourself is “Does this look like the sort of person that you would think would have a radar detector?” This is the easiest place to hide camera. A $30 hotwheels radar gun is looking kind of useful.