I like this part.
"The sheriff's office warns motorists should consider using precautions when an officer in an unmarked vehicle is conducting a traffic stop. Look for an official uniform, department identification, and badge. If something doesn't feel right, call 911."
http://www.kare11.com/rss/article/953742/14/Man-impersonating-police-officer-makes-traffic-stop-in-NW-metro-