Unmarked vehicles are becoming more commonplace. The CA CHP has some that are unmarked except for a very faint emblem on their doors so you can tell they are legit when their door opens, even if it is an older green metallic Dodge Ram pickup.
The local city police has some really POS car I suspect they use for narcotics or undercover work. Fenders are gray primered and different colors on body panels and dents too. It does have a siren and the colored lights buried in the grill, but you'd think it would never be a police officer so I could understand some people's apprehension on pulling over and I've never seen him use it for traffic, but maybe it's just used for going to a call. He had the siren on at an intersection with the lights on and it sure was a bewildering site until I caught a glimpse of his uniform. Then again, maybe he was a fraud too?
Arizona is getting more unmarked vehicles too and it was a subject on the radio yesterday, plus a lot of speed cameras. It was a side-bar in my last months Auto Club magazine as well. Danica Patrick (Indy car) has been busted for 50 in 35 twice in Scottsdale, AZ off their cams. Her reflexes alone ought to give her a pass and maybe she'd get off if it were a cop rather than their speed cams.
I was just looking at the town of Maricopa, CA on Speedtrap.org where it appears their local cops will write you for 20 over even if you are under the limit. Money must be needed in a town of only 1100 people (looks like it has maybe 200 at best when I went through there. Pretty much a ghost town except for one mini-market and one restaurant).
Here: Speedtrap.org - Maricopa, CA speedtrap
Pendergrass, Georgia is another big trap one where the average citizen there pays over $1,136 a year for local traffic fines (pop. of 450 people). I read where Illinois is also seeking fines of $1000 for on-cam speeding and pushing for $2000 in Maryland. Probably will only go up as average income/wealth drops.