如有…请 / 如需…请【rú yǒu … qǐng / rú xū … qǐng】

如有…，请… is how notices, signs and service messages tell the reader what to do if something comes up. 如 is the written form of 如果, and the condition has no subject: it applies to whoever is reading.

如需 and 如遇

如需 is "if you need", and 如遇 "in the event of". Both take the same 请 clause.

Without 请

The second clause doesn't have to be a request. In rules and contracts it states what will happen.

No subject after 如

如有 is a fixed two-character opening. To name who has the problem, go back to 如果.

• × 如你有问题，请举手。 → 如有问题，请举手。 / 如果你有问题，请举手。
• × 如有问题的话，请举手。 → 如有问题，请举手。