They do if they think someone is impersonating a police officer and has a gun. They love to shoot at people, its like 45% of their job depending on the area. Seriously, this would work. Given that we have a case fresh in the minds of someone impersonating a police officer and assassination people, they'll take you seriously. Hell, tell the 911 operator that you're a republican and the police might even run some red lights to get there.

Edit: in all seriousness though. This is solid advice. Police dont like other people pretending to be them.