Hazardous warning diamonds are labels that indicate the presence of hazardous materials, such as chemicals, flammable liquids, explosives, and radioactive materials. These labels usually consist of a four-color diamond-shaped symbol that is divided into quadrants. Each quadrant is color-coded to represent a different type of hazard: blue for health hazards, red for flammability, yellow for reactivity, and white for other specific hazards.

The use of hazardous warning diamonds is mandated by various international and national regulations, such as the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) and the United Nations' Recommendations on the Transport of Dangerous Goods. These labels help ensure the safe handling, transport, and storage of hazardous materials, and provide important information for emergency responders in case of an accident or spill.