I go by state law. There are far too many signs up to stop and read them all. As far as shoes and shirts go, they are visual issues, usually to keep out the beachcomber or under dressed, guns are concealed in my state. We have discussed this issue many times and the search feature can be your friend. If you aren't allowed by law that's one thing, but any idiot can put up a sign anyware they please, so how is a person to know who put the sign up, and if it is the wish of the owner.
I sure don't give a hoot about what 17 year old manager thinks about my rights, do you?
If the law says no that's one thing, but a sign can be put up by anyone.
Winn Dixie had a "no handgun" sign down in Boca about 12 years ago, they had to remove it. The State told them they had no legal way to enforce it. Again it depends on where you live.