ANSI Z535 series of standards recognize five types of signs: danger signs, warning signs, caution signs, notice signs, and safety instruction signs.
Danger signs feature a white text on a red background and should be used for the most dangerous hazards in the workplace.
Warning signs feature a black text on an orange background and signifies there is a serious hazard in a work area.
Caution signs feature a black text on a yellow background and are used for hazardous situations that may result in minor or moderate injury.
Notice signs feature a white text on a blue background and designed to relay other information not related to safety and when there is no imminent hazard in the area.
Safety instruction signs feature a white text on a green background and convey safety-related information.