I had the VIN checked during a traffic stop while on a classic motorcycle, and the officer even cross-checked the engine VIN and the frame VIN. This was in a small town in PA.
I've had customers in the past who were pulled over in cars from the '50's.
Once the officer noticed there's no VIN tag in the dash right under the registration sticker and inspection sticker, it's usually a red flag, especially since a majority of stops are done on newer cars. The officers have even asked as to where the VIN tag is. Once they open the door and show them it's riveted on the jamb, then numbers are taken a look at to make sure.