KMA-628 is the old FCC callsign for the Los Angeles County Sheriff's Department. Similarly, KMA-367 is LAPD.
Not really used much these days, but if you drive around in L.A. and see "Los Angeles" on the top of a license plate frame and "KMA-628" on the bottom of the license plate frame, the person driving the car was usually a cop.
I took mine off my car in 1990 when criminals learned what it meant and started shooting at cars with KMA-628 or KMA-367.