Learn Dutch: Er is hier geen uitgang. - There is no exit here.

The bare infinitive on signs is used for commands or instructions (like Niet roken for "Do not smoke"). This sentence isn't giving an instruction; it simply states a fact ("There is no exit"). If a sign wanted to give a command like "Do not exit here," it might use an infinitive like Hier niet naar buiten gaan.

Could I start this sentence with hier instead of er?

Yes, you can say Hier is geen uitgang. Starting with er (there) is the standard way to state that something exists. Starting with hier places a bit more emphasis on the location: "Here, there is no exit." Notice that because Dutch uses V2 (verb-second) word order, the verb is stays in the second position either way.

Why do we use geen instead of niet to say "no exit"?

Geen is used to negate nouns that are indefinite (nouns that would use "a" or "an" in a positive sentence). Because the positive version of this sentence is Er is hier een uitgang (There is an exit here), you negate it by replacing een with geen. You use niet when negating verbs, adjectives, or specific things (like "the" exit).

If uitgang means exit, how do you say "entrance"?