Red signs are Prohibition signs.
A sign prohibiting behaviour likely to increase or cause danger, such as a No Entry sign. Red is also used to identify and locate fire-fighting equipment.
Yellow signs are warning signs.
A sign giving warning of a hazard or danger, such as a laser radiation sign.
Blue signs are mandatory signs.
A sign giving specific action to be taken, such as the wearing of personal protective equipment.
Green signs are Emergency Escape and First Aid signs.
A sign giving information on emergency exits, escape routes, first aid or rescue facilities.