I based my comments on my experiences of how demonstrator and similar vehicles are transported throughout the UK other than on a transporter.
If you get a chance to see, for instance, a Ford demonstrator vehicle it is fully battenburged with police markings and operational blue lights. The crest on the door, however, is the standard Englandshire Police badge surrounded with 'Ford Demonstration Vehicle' or similar, rather than 'Somewhere Constabulary'.
These vehicles have the roof bars covered with a tailor made white bag and the Police on bonnet and rear covered with a flexy magnetic blank when driven bt Ford employees and not in active police use.
Similar has also been done when police vehicles have been driven from their home constabulary to shows in the south of England or back to BMW for warranty replair.
Just my tuppence...
Good looking project, by the way. Theres always a market for working (ex) police vehicles for film and similar use, apparently.