Hazard symbol

Skull and crossbones, a common symbol for poison and other sources of lethal danger (GHS hazard pictograms)

Hazard symbols or warning symbols are recognisable symbols designed to warn about hazardous or dangerous materials, locations, or objects, including electromagnetic fields, electric currents; harsh, toxic or unstable chemicals (acids, poisons, explosives); and radioactivity. The use of hazard symbols is often regulated by law and directed by standards organizations. Hazard symbols may appear with different colors, backgrounds, borders, and supplemental information in order to specify the type of hazard and the level of threat (for example, toxicity classes). Warning symbols are used in many places in place of or in addition to written warnings as they are quickly recognized (faster than reading a written warning) and more universally understood, as the same symbol can be recognized as having the same meaning to speakers of different languages.[citation needed]

Navigational hazards are generally marked on nautical charts, and are also often marked by moored buoys, and changes are published in notices to mariners.