It appears to be a GE MASTR model, produced from 1964-1973. I would guess, since the faceplate has
LA Co. Sheriff printed on it, more than likely it was custom built for them. Being that it's plastic it makes it a later version, earlier models were die cast metal instead. Here is a link I found that has some information.
http://www.wb6nvh.com/GE/GEhist2.htm MASTR series is at the bottom of the page.