So, under the pretext of confidential investigative purposes, you can be pulled over by unmarked police vehicle, as interpret-ability of this law is very vague.
In most jurisdictions, it is illegal for anyone but a police officer (or other classes of first responders) to operate lights and sirens.
What does an unmarked police car look like?
If you look closely at some unmarked police cars, you’ll see light bars built into the front grille.Sometimes there will be lights at the top of the dashboard, as well. Usually you won’t see these until it’s too late and they’re flashing red and blue in your rearview mirror.
How can you tell if a car is undercover?
Spot an UNDERCOVER POLICE CAR?! –
Why do police use unmarked cars?
Unmarked cars are not as easily identified as a generic police car, this is beneficial to the police as the officers are able to observe motorists acting naturally (as opposed to them changing their driving habits because they are aware of the presence of a patrol car).
Photo in the article by “Flickr”