Be nice or I'll zap you both with my super mod zapper.
As for the origianl question? Drive to a well lit, populated area. Drive at the speed limit and don't make evasive maneuvers that might cause the cop (if he is one) to pit you in an effort to terminate a pursuit.
Once you ID the cop as being legit, explain to him politely that you were concerned about his unmarked car and had been told to respond the way you did.
If they weren't legit, they would probably bug out once they realized they had an audience.