Fire safety signage is not one category but four, and the colour tells you which you are looking at before you have read anything. Red means fire equipment. Green means a safe condition or escape. Blue means a mandatory action. Yellow means warning. Reading a building's signage is faster once you know the colour is doing the work.
Red: fire equipment
Signs identifying and locating firefighting equipment are red with white symbols. That covers the fire alarm call point sign, extinguisher signs, hose reel signs, fire blanket signs and hydrant signs. Red is reserved for fire equipment and for prohibition signs, which is why an escape sign is never red and why a red sign near an exit is identifying an extinguisher rather than the way out.
Green: safe condition and escape
Escape route signs, exit signs, assembly point signs and first aid signs are green with white symbols, indicating a safe condition. This is the category most people mean when they say fire signs. The green and red distinction is the single most useful thing to know about fire signage, because it separates the way out from the equipment in one glance.
Blue and yellow
Blue circular signs are mandatory: fire door keep shut, fire door keep locked, and similar instructions telling somebody what they must do. Yellow triangular signs are warnings, used for hazards such as flammable materials or high voltage. Both appear routinely in fire safety signage and neither is an escape sign, which is why a blue fire door sign is not telling you where to go.
Signs that are not doing anything
The common failures are a sign in the wrong category, a sign that has been painted over, a sign hidden behind a notice board or stock, and a sign carried over from a previous layout pointing at a wall. The last is the worst, because people will follow it. Walking a building as a stranger, looking only at signs, finds all four faster than any checklist.
Questions people ask about categories of fire signage
What colour is the fire alarm sign?
Red with a white symbol, because signs identifying firefighting equipment including call points are in the fire equipment category. Escape signs are green.
What are the categories of fire signage?
Fire equipment signs in red, escape and safe condition signs in green, mandatory signs in blue and warning signs in yellow. The colour identifies the category before the symbol is read.
Why is a fire door sign blue?
Because it is a mandatory instruction, telling you what you must do with the door, rather than an escape sign showing where to go.