Just because he was driving a car? He never said he was a cop?
Case dismissed.
How many dogs did he shoot?
Foe example, you could buy and drive a dark gray Crown Victoria and have a searchlight mounted on the driver door.
It wouldn't have any police markings, but 100% of the people you pulled up behind would think you were an unmarked police cruiser.
You could even wear a hat that would look something like a state police hat, something purchased in an ordinary store.
I posit that you would not be actually breaking the law, but you would be affecting other drivers’ behavior.
Search for the case of “The Red Light Bandit” aka Caryl Chessman...
http://en.wikipedia.org/wiki/Caryl_Chessman
My father was an arresting officer in that case.