This post has been updated. See new photograph below.
North Coast Co-op just doesn’t have the same friendly vibe as People’s Co-op in Portland. Luckily, there’s Wildberries Market in Arcata as well, and Eureka has at least one natural foods store. 
There don’t seem to be any public restrooms in or near Arcata Plaza, so perhaps North Coast is the closest restroom. I’m sure there are good reasons for the restriction, but still, I always feel alienated by such signs, or the ones that say, “We reserve the right to refuse service to anyone.”
***
If you look at the comments on this post, you’ll notice that David, the manager of the co-op, chimed in. Since I posted the photo above, the store has toned down the door a bit. It looks better now, though I think the “backpacks” sign could still be improved. I’m impressed that the staff at North Coast is so willing to make changes in response to customer feedback. 
I agree. I even hate to see “No Trespassing” signs. I know there is a reason for them, but they feel so unfriendly.
Hi from North Coast Co-op: I’m the General Manager and I understand how you feel. These restrictions were just put in place a few weeks ago because we really had no other choice. The restroom was being totally over-used, abused, vandalized and made unusable. I wouldn’t want to describe the stuff that our employees have had to deal with! While we are not altogether comfortable with excluding anyone, it isn’t fair for our members and shoppers to absorb the costs, or for our employees to do the dirty work, because the City of Arcata hasn’t met their responsibilities to provide convenient public restroom facilities. Looking at the picture, though, we can probably do with fewer signs that all say “NO”.
David, thank you for commenting on this post. Of course, it’s easy for me to comment on the signs; I don’t live or work here and don’t have to deal with the daily problems. I assumed that your bathroom was probably the closest to the Plaza and got a lot of use, and that’s why North Coast had adopted this policy. I did notice that the city didn’t seem to have provided any public restrooms, and I wondered about that. I agree that the local businesses shouldn’t have to take up all the slack. But fewer signs on the door probably wouldn’t hurt.
Beth – We’ve made that change. Thanks for helping us to see what should have been obvious!