By Kim Glovas, Oren Liebermann

PHILADELPHIA (CBS) - Two separate reports of people impersonating police officers have prompted a warning from the Philadelphia police department. Both incidents happened Wednesday night in the Northeast.

In the 7-11 parking lot in Holmesburg, the Toyota Camry was unmarked, but police say the driver impersonated an officer when he pulled over another car Wednesday night.

“I walked up and I just saw an unmarked van and two cruisers,” said eyewitness Jim Doughty.

Doughty saw what happened next, when two real officers spotted the impersonator and arrested Julian Collins, 22.

3 On Your Side wanted to know what you do if you suspect you are being pulled over by someone pretending to be police.

“If I know it’s not a cop, I’m not pulling over,” said Doughty. “They gotta have flashing lights to pull me over.”

But police say these impersonators did have flashing lights. In another case of police impersonation Wednesday night, two suspects carried fake badges. One even wore a shirt that read police.

Police Lieutenant John Stanford says the two men stopped a car at 9:30 in the Holmesburg section of the city, pulled guns, and forced the driver and two passengers into the back seat. The three managed to escape but without cell phones.

The two suspects were driving a truck with red and blue flashing lights. Stanford explains what to do if you are unsure of the situation.

“Do not hesitate to call 9-1-1. If you have a cell phone call 9-1-1. Give your location. Give a description of the individual stopping you and tell the 9-1-1 dispatcher that you are requesting a marked unit. “

Stay on the phone with 911 and ask for a marked police car. All police officers carry a badge and Philadelphia police identification card. Ask to see it to be sure.

“Stay inside your vehicle until a marked vehicle arrives and you are sure that it is actually a police officer,” said Lt. Stanford