What and who are the postal police?

Matt:

I've been meaning to ask this for a long time. It's bugged me. I remember seeing a car screaming past me on the freeway one day that had wire mesh screen between the front and back seats, and on the side it said "Postal Police." Postal Police? Who's that?

-- VV, Chula Vista

They're the muscle for the postal inspector's office. Got a mail-bomb threat? Fistfight at the parcel post window? Undercover UPS operatives trying to sneak in the employees' entrance? Call the postal police. They're security guards at post offices who check IDs, keep the peace, and haul off postal felons. We have a dozen or so in the county. Feel better now?