Questions & Answers about A regra é simples: não se permite fumar aqui.
Why is se used in não se permite?
Why does se come before the verb here (não se permite) instead of attaching to the end?
In European Portuguese, pronouns normally attach to the end of the verb. However, negative words like não act as "magnets" that pull the pronoun directly in front of the verb. If the sentence were positive, it would be permite-se, but the não forces it to be não se permite.
Why is the infinitive verb fumar (to smoke) used to mean "smoking"?
In Portuguese, the unconjugated infinitive form of a verb (like fumar) is used to talk about an action as a general concept. Where English often uses an "-ing" noun (like "smoking" or "swimming"), Portuguese just uses the infinitive.