I've seen a pic of an unmarked Caprice in an LAPD group on flickr a while ago: https://www.flickr.com/photos/26423305@N00/22634288223/
There's also a pic of another unmarked Caprice with a Spectralux: https://www.flickr.com/photos/146280704@N07/31996010736/
I haven't seen any pictures or videos of unmarked LASD cars with a Spectralux, so my best guess is LAPD. It's most likely a 9C3 though, so I'd guess it's used either for detectives or administrative uses. Either way, it's probably rare.