I believe the police should question someone at least for a carry permit,
Have you ever read the US Supreme court decision on Prouse v Deleware?
Random stops to check licenses are illegal. Doesn't matter if it is becasue you are driving a car, or OCing...that is as you are assuming you need a license to OC. You do not need a license to OC in 29 states, including WA where I live.
You must be presuming that OC is an unlawful activity...or that it "may" be lawful only if you have a license...the law does not work that way. You are to be presumed innocent, unless proven guilty...you are also to be secure in you private affairs, unless you have done something openly unlawful, and LE can get a warrent for it.
I have OC'd since 1970, and have never been hasseled, I did have one time where someone had open stated he was going to beat me to a pulp (I have no idea why) until he noticed I was armed. and then he could not leave the area fast enough. My carry never left it's holster, but he left and I was safe, that is what counts.
My experience has been, OC and you do not have to worry...the criminals will just go looking for someone that has a much lower likelyhook of doing Them harm.