In Poland police is allowed to pull people over from unmarked cars (they are general cars with full police equipment inside. Policeman must be in his complete outfit). It's nearly impossible to distinguish them from normal cars (except all have powerfull engines). They can stop you day/night in city and day only outside city. In Germany I was stopped once by German Border Control near Austria/Germany border on the highway at about 11:00 pm. I was pretty scared where was this speed limit sign that I missed (I was doing 70 kmh on a very heavy rain). They were driving in silver BMW 7 without any marks (except POLICE - FOLLOW US on the rear window). They just checked our documents, asked where are we going to and let us go.
In California, a legal emergency setup is: a forward solid burning red light and a flashing amber light on the rear. If they dont have that, I dont move over.
