There's all kinds of callsigns for the "new" (mostly UHF-T, mostly
digital) LAPD dispatch frequencies. KMA367 was THE callsign fom 1948
into the late 1950s, and is still in existence for a handful of
mostly-seldom-used freqs.

"KMA" is merely a shorthand for KMA367 that developed over the years
when officers (not dispatchers) would indicate that they were finishedd
with a relatively lengthy message.

It's still used out of habit, even though the KMA367 callsign hasn't
been used for patrol frequencies in almost 22 years.
Harry
http://users.snowcrest.net/marnells/kma367-1.htm