Unmarked cars are a lot more subtle than they used to be. Most of the stuff is hidden from view now.
This, Quite a selection of cars used in Hertforshire and Beds too, Once or twice the odd thing will give it away like a shark-fin aerial for factory radio, with an additional aerial near it. Lights are usually very well hidden and so many cars have dash-cams now , that isn't a give-away either anymore.