I did a quick search and found this info. I can't guarantee it's 100% correct but I hope it helps.
"On Mopar's from the early 60's until the mid-60's VIN numbers were all numbers and the way to tell a police car was if the second digit was a "9". This meant that the car was a police package. In 1966 they changed this so that if you got a police package the second digit was a "K". So, if you had a 1967 Plymouth Fury that was a police car, the VIN would start out "PK", P for Plymouth, K for Police. They used this method until 1977 and is the easiest way to tell if it is a factory police package car.
This is an example of a 1969 Plymouth Fury. The VIN started with "PK41" which means Plymouth, Police Package, 4 door Sedan
The second way you can ID a police car is if it has the "A38" package. All Chrysler, Dodge, and Plymouth cars have what is called a fender tag. This was a tag that was screwed onto either the inner driver side fender or on the radiator support just in front the battery. If you see an "A38" on the tag that means it was a police package car. This was available starting in 1970. Some cars, such as the 1976 Dodge Dart and 1976 Plymouth Valiant, were available as a police package but only with the A38 package, they could not have the "K" code in the VIN.
The last way to ID a police car gets more complicated. Not all agencies ordered a police package car. Some ordered a normal car then added all the cop options to it. Two agencies known for this were the Washington State Patrol and the North Carolina Highway Patrol. Will give you an example, since we own a 1972 Dodge Polara that served with the WSP. Our 72 is not a police package car, but it is a real police car. How do we know this? Couple of things to look for. It has a factory spotlight and certified speedo (verified by the fender tag and the build sheet, which is a piece of paper that went with the car and shows every option available on the car). It is also a special ordered car, with Y39 on the fender tag and a second "special order" tag next to the fender tag. This does not mean it was definitely a police by car itself, but it is a good sign. It also has the roof reinforcement, extra welds on the body, etc, etc. It can be hard to spot these cars, but they are as much a police car as one with an "A38" on the fender tag or a K as the second digit of the VIN.
