There are several ways to express запрещение (the prohibition) of doing things. The easiest way is to use the verb запрещать/запретить (to forbid):
Another way for the prohibition is to use the predicate нельзя (it is not allowed, it is forbidden). Нельзя is the negative form of можно (it is allowed).
With the predicate нельзя, if you want to mention the person who is not allowed to do something, then that person goes in the dative case:
But you can encounter other signs in the city, telling you what not to do. For example by using the verb ставить/поставить (to place, to park):
There are also some ways to forbid things in a not-so-direct way. If you look at the photo below you can see the following sign:
(Dear Muscovites and guest of our capital! We have an earnest request – don’t walk on the grass!)
As you can see, in Russia rules are made to be broken!
More grammar rules, prohibitions, and expressions you can find in Self-study section.