When you go into a restaurant and see a sign that says "No Dogs Allowed," you might think that sign is purely proscriptive: Mr. Restaurant doesn't like dogs around, so when he built the restaurant he put up that sign.
If that was all that was going on, there would also be a "No Snakes" sign; after all, nobody likes snakes. And a "No Elephants" sign, because they break the chairs when they sit down.
The real reason that sign is there is historical: it is a historical marker that indicates that people used to try to bring their dogs into the restaurant.
Most prohibitive signs are there because the proprietors of an establishment were sick and tired of people doing x, so they made a sign asking them to please not. If you go into ...