A word of caution. I wouldn't trust the police here. Police will sometimes tell you something is illegal when they know it isn't. They think the law *should* be one way rather than another, for example. Or they are simply mistaken.

If WA's statute is like those in other states, it does not rule out more than blinkie. In that case, even if the police are telling you otherwise, they are mistaken.

Why don't you post the text of the law itself?

Before anyone starts saying that we shouldn't give "legal advice", bear in mind that the police will be the first to tell you that they do not give legal advice. The police's interpretation of the law has no official weight, as you would discover if you ever relied on an incorrect interpretation of some law offered by a police officer and faced charges anyway. (It's not going to happen in this case, but it has happened in other, more serious, matters, like gun possession crimes, or tax evasion, where the law can be quite obscure.)

No one here should offer you legal advice, that is, authoritative comments on how to conduct legal proceedings, but anyone can read for himself.