Police in Mesa County, Colorado received the first authorization ever for police to fly UAS. That was last year. Since then, a county in Florida received authorization. Police in Texas toyed with the idea, but decided it wasn't in the budget. So i know of precisely two police precincts with legal authorization. It's possible there's a couple others I haven't heard about, but the total number is still very small. Even the Utah Highway Patrol got slapped down by the FAA for flying without authorization.
M. Wilson at the FAA has denied applications for certificates of authorization (COAs). Without his signature, the popo doesn't get to fly.