Write an article based on this "Check to see if it's a marked vehicle. Identify the vehicle's make and model. Call 911 while you're being pulled over. Learn your state's laws."
If the vehicle has police markings, it is highly unlikely that it would be an imposter. A civilian driving a marked police vehicle would most likely be spotted very quickly by an actual police officer, and that individual would quickly get arrested for impersonating an officer. If a marked police vehicle is attempting to pull you over, it's generally safe to assume that that individual is a real police officer. If the vehicle is not clearly marked as a police vehicle, you'll need to identify what make and model the vehicle is. Police officers in the United States generally only drive a limited number of vehicle makes and models, and those vehicles are usually in decent shape (though they may be scratched up or lightly dented from previous pursuits).  Police sedans in the United States are almost always a Ford Crown Victoria, a Chevy Impala, a Dodge Intrepid, a Dodge Charger, or a Chevy Lumina. Police SUVs are almost always a Ford F150, a Chevy Tahoe, or a Dodge Durango. Most police departments use relatively new vehicles. If the vehicle pursuing you looks old and/or very broken down, it may not be a real police vehicle. If you're still not sure whether it's a real police officer, the best thing to do is to call 911. Try to give the dispatcher a detailed location of where you are and a description of your vehicle and the alleged police vehicle. The 911 dispatcher will be able to use that information to check with the local police or sheriff's department to determine whether the vehicle you're being pulled over by is actually a police vehicle, and whether that officer has actually pulled you over. Be sure to give the make, model, and license plate of both your vehicle and the vehicle you're being pulled over by. Though some states permit unmarked police vehicles to conduct routine traffic stops, some states have outlawed this practice. In New York State, for example, unmarked vehicles are no longer allowed to stop motorists for routine traffic violations (though certain exceptions may be made). Other municipalities have very strict rules on whether a plain-clothes officer can conduct traffic stops, regardless of the vehicle that he or she is driving. Search online to find out whether unmarked and/or plain-clothes traffic stops are permitted in your state, county, or city. You can also call your local police or sheriff's department to find out about their policies on unmarked vehicles.