By Marianne Martinez, CBS 11 News

DALLAS (CBSDFW.COM) – North Texas law officers are issuing a warning about fake cops. An increasing number of police impersonators have been caught on area streets, and authorities are particularly concerned about two recent incidents in Dallas.

Two off-duty officers with the Dallas Police Department were recently pulled over by two different police impersonators. One of the fake cops was a security guard. The other was a former Cockrell Hill fire chief. Both impersonators were arrested and now face felony charges for impersonating a public servant.

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According to actual law enforcement officers, these fake cops can often look like the real deal. Many drive around in vehicles with flashing lights, and wear uniforms that resemble those of a real officer. Sometimes, they even carry guns.

Authorities fear that the police impersonators will rob and grope their victims, and maybe even do something more serious.

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Back in December 2009, CBS 11 News spoke with the mother of a teenage girl, who said that her daughter was pulled over at the intersection of Samuell Boulevard and Jim Miller Road in Dallas. A fake cop proceeded to grope the girl, but the teen managed to get away before things got worse.

And in August 2008, a man dressed as a police officer at the Fort Worth Stockyards was actually a parking attendant and a registered sex offender. That man was arrested.

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If you ever suspect that you are being targeted by a fake police officer, do not get out of your car. Go to a well-lit, heavily-populated area and call 911 to speak with the dispatcher about the situation. Real police officers must call dispatchers every time someone is pulled over.