Most cop cars were the most basic cars you could buy. For example, in a B-Body Plymouth, this was a Belvedere. In a C-Body Plymouth, this was a Fury I. But the VIN's on those cars are different from a Fury I or a Belvedere, the second digit in the VIN is a K. So, for example, a 1969 Belvedere Police with a 383-4 barrel would have a VIN starting as RK41H9. That would be the first thing to notice in decoding a police car.
Now, you may ask why my cop car isn't that way. I cannot say why, but it is pretty obvious the department that ordered my car wanted an unmarked car with more "trim", so they ordered a Satellite, hence the reason my VIN starts as RH41N0. I have seen this on a PA State Police 1972 Fury II. Apparently, the PA State Police wanted something more "plush" than a Fury I, so they custom ordered their cars with the police equipment. It looks to me like the same thing happened to my car, except my car doesn't have the A38 Police Package on it, which is interesting to me. Maybe it wasn't availible on a 1970 Satellite, so it was just special ordered with Cop Car options?
Here is the fender tag off of my Satellite. It is a Lynch Road fender tag, so there isn't much info there, but what first tipped me off that this was a Cop Car is the J in front of the dealer order number, which means that the car was special ordered. Also, the "26" stands for a 26" Radiator and that normally wouldn't come on a non-A/C car like mine.
Here is the build sheet I found in my Satellite. The VIN and dealer order number are both exactly three off, so I have to assume both were ordered by the same police department, or at least by the same dealer. There are only minor differences between my car and this one, plus I know some additions have been added to my car, like a radio. I don't think you can see it in the pictures, but looks to me like the original radio delete plate was cut up for the current radio in the car.