A hazard symbol or warning symbol is a recognizable symbol designed to warn of a hazard or hazardous material, location, or object, including current, poison, and radioactivity. The use of hazard symbols is usually regulated by law and directed by standards organizations. Hazard symbols may appear in different colors, backgrounds, borders, and supplemental information to specify the type of hazard and the level of threat (e.g., toxicity category). Warning symbols are quickly recognized (faster than reading written warnings) and easier to understand (for users of different languages, the same symbol can be understood as having the same meaning), and they are replaced or used as written warnings in many places.

Biohazard markers are used to label biomaterials with significant health risks (biohazards), including virus samples and used hypodermic needles.

The biohazard mark was developed by Dow Chemical Company for its container products in 1966.

According to Charles Baldwin, who contributed to the development of the environment, "we want something unforgettable but meaningless, so we can teach people what it means." In Science in 1967, the symbol was the new standard for all biological hazards ("biohazards"). The article explains that Dow artists have drawn more than 40 symbols, and all the symbols studied must conform to many standards: "(I) eye-catching form to attract immediate attention; (II) unique and clear, in order not to be confused with symbols used for other purposes; (III) easy to identify and recall; (I V) easy to make templates; (V) symmetrical, so as to be the same from all perspectives ; and (VI) people of different ethnic backgrounds accepted by the group. " The selected people scored the highest on the national memory test.