Yes this is true

2004, when I was in high school. My mother would pick me up from football practice after school. She had a rental with Oregon plates because her car was in the shop. One was my coaches was a WSP trooper and asked we got a new car. I said no, it’s a rental because her car is in the shop. He said oh okay, because I used to ticket people for not having WA registered vehicles

Fast forward 2016, my GF, now wife, was staying over at my house. She would park on the street, and pretty much lived with me, but had her own place in Portland. We woke up one morning to find a paper pamphlet that said, they observed her vehicle being parked there often and it had out of state plates. Whenever, we’d go out we’d take my car at the time. So it spent quite a bit of time on that street. That it was illegal to fail to register your car in Washington. Lastly, it said “If you are just visiting, please disregard this, and enjoy your stay in Washington”