Yesterday I was eating in a downtown area. I probably saw 8/10 people walking down the sidewalk with masks on.
I'm considering publicly shaming them, since that's what gets them to wear a mask in the first place.
In college, we used to drive around and ask "Do you know where the library is?". If they knew, we'd just shout "NERD" and drive away. Completely immature and stupid, but I wonder if a similar tactic would wake a few people up.
Use gromets. Highlights the stupidity, but complies enough to get past the register. Or don't use anything, but carry around post-its for emergency compliance.