Someone impersonating a police officer is stopping drivers in Williamson County. The Williamson County Sheriff's office is advising the public of a blue SUV using red and green overhead flashing lights that tries to pull drivers over in the Liberty Hill area. A tweet this Tuesday by Sheriff Robert Chody says if anyone confronts such a situation to pull over and stop, activate the vehicle's emergency flashers and to call 9-1-1 and report what's happening. Sheriff Chody says the SUV driver is an impersonator because green is not a color of lights used on law enforcement vehicles.