Warning sign may refer to:
- A traffic warning sign is a type of sign which indicates a potential hazard, obstacle or condition requiring special attention
- Safety sign, a sign that warns of a hazard, prohibited action, required action or equipment, and locations of safety equipment or exits
- Hazard symbol, recognisable symbols designed to warn about hazardous or dangerous materials, locations, or objects
- Warning label, label attached to a product (such as chemicals or tobacco) warning the user about risks associated with its use