Usually when you see bright blue lights in your rear view mirror, it's a police officer signaling you to pull over, but now that might not be the case.

The Soddy Daisy Police Department is warning residents about criminals posing as officers in unmarked cars with police lights. Their warning comes after Memphis Police say a woman was pulled over by three fake police officers who robbed her at gunpoint. They say the suspects were driving two vehicles equipped with police lights. 

"They are impersonating a police officer which is a crime. When that happens that's where the safety factor comes in is you don't know really who is pulling you over," said Sgt. Jerry Workman, with the Soddy Daisy Police Department. 

This is the first time Workman has heard of this type of crime in his 22 years of law enforcement experience, but he says buying police equipment in stores and online is becoming easier. A quick Google search shows police dashboard lights selling for less than 20 bucks. 

"Some of them may or may not check to see if you're legit," said Workman. 

It's why workman and other officers want you to know what to look out for. 

"The markings on the car should say Soddy Daisy Police Department; should have the police agency that's pulling you over. Now if it's an unmarked car it's not going to have any writing on it," said Workman.

In that case, Workman says to pay attention to the lights on the car. He says most official police cars have up to eight sets of lights in the front, some in the back and sometimes on the sides of the car. However, the color of police lights vary. In Hamilton County, Workman says they should be blue. 

"Now if the blue lights are on top of the car more than likely you've got a 100% police officer." 

Workman says that criminals will rarely be caught with top lights because they are typically more expensive. 

Though the details are important, pulling over in a well lit area will also make a difference. 

"A Walmart, a restaurant that's open 24 hours, a convenient store; while you're going call 911 and just verify that that is a true police car behind you," said Workman. 

Soddy Daisy police officers say there have been no similar incidents in the area, but if you find yourself  in that situation or become skeptical call 911.