That’s odd my next-door neighbor is a Washington state highway patrol officer and he tells differently.
You are assuming that the police know the law. I would find the statute, print it out, and keep it in the car. Even then you might get a ticket that you would have to go to court to fight. A few years ago 3 of us old geezers were riding our Triumphs to a charity event. We were riding single file and this...Peace Officer... at some risk to our safety tailgated us for 5 miles. He then jammed his cruiser in between us, one at a time tailgating each of us. He then got back behind the last man in formation. We had on full gear, no club patches, quiet pipes, and were breaking no laws. After a 30 minute, rude inspection of all our bikes, he wrote one guy up for having a vertical license plate. We didnt think it was a violation. He said it made the plate unreadable! I though, to myself, that he must not go to the Library! Anyway my friend went home and looked it up and orientation of the plate is mentioned nowhere in the statute! Ignorance of the law is no excuse, if you are only a citizen. This fuy was out to write someone up. It didnt matter to him that he had to invent a law to do it.