a message informing of danger

cautionary advice about something imminent (especially imminent danger or other unpleasantness)

notification of something, usually in advance

serving to warn

a bell used to sound an alarm

conspicuous coloration or markings of an animal serving to warn off predators

a device that signals the occurrence of some undesirable event

a cautionary sign of danger

a warning to national policy makers that an enemy intends to launch an attack in the near future

a warning to national policy makers that an enemy intends war or is preparing for war and is on a course that increases the risk of war

an automatic signal (usually a sound) warning of danger