Several weeks ago I passed this restroom door, which was located in a grocery store.
Cannot? Oh yeah? That sign made me want to prove the sign wrong by carrying tons of merchandise into the restroom until it was completely full of merchandise.
I don’t know why the “can” vs. “may” error gripes me so much–perhaps it’s because I hear and see this problem so often, and also because it seems that it would be so very easy to understand the problem and stop making the error.
Of course, “may” comes from the same root word as “might” and originally meant that it is in your power to do so. The specialization for having permission is rather late.