There are several ways to express запрещение (the prohibition) of doing things. The easiest way is to use the verb запрещать/запретить (to forbid):
въезд запрещён (no entry)
фото- и видеосъёмка запрещены (no photographing or video filming permitted)
выход на лёд запрещён (it is forbidden to walk on the ice)
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).
здесь курить нельзя (it is forbidden to smoke here)
туда нельзя! (you can’t go in there!)
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:
вам нельзя говорить громко в библиотеке (you are not allowed to speak aloud in the library)
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):
машины не ставить! (no parking!)
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:
Уважаемые москвичи и гости столицы! Убедительная просьба – на газоны не заходить! (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!
