If a convenience store says "No Shirt, No Shoes, No Service", no reasonable worker would refuse service to someone wearing a dress.
Odds are good they will if they disapprove of the dress, or if they disapprove of the someone’s wearing of a dress.
Because the rule is not actually about shirts or shoes, it’s about throwing out people considered undesirable. Those signs were invented to throw out hippies.
Similarly “please wait to be seated”, used to be only in high-end restaurants, lower end ones introduced them so they could ignore / refuse to seat hippies. It’s much easier to make a patron leave when they’ve been standing at the entrance for half an hour than when they’ve seated themselves.