Safety signs are regulated by shape and colour so that meaning survives language, distance and smoke. For fire purposes there are four categories in general use, and the reason a sign looks the way it does is that the shape carries the category before the pictogram carries the detail.
The four categories
Prohibition signs are round, red bordered with a diagonal bar, and forbid something: no smoking, do not use lift in event of fire. Warning signs are triangular and yellow, and identify a hazard: flammable material, explosive atmosphere. Mandatory signs are round and blue, and require an action: fire door keep shut. Safe condition signs are rectangular and green, and identify escape routes, exits and first aid. Fire equipment signs are rectangular and red, and identify where equipment is.
Why the shape matters more than the words
Shape and colour are readable at a distance and through smoke long after text has become unreadable, and they work for people who do not read English. Regulations require signs to comply with the specified shapes and colours precisely so that this holds, and a well meant custom sign in the wrong colour breaks it.
The two that get confused
Green is safe condition and red is fire equipment, and both are rectangular. Green tells you where to go. Red tells you where a thing is. A green sign over an extinguisher and a red one over an exit would be a serious error, and it happens in buildings where somebody has bought signs by appearance.
Supplementary text and arrows
Text below a pictogram is supplementary and is there to make the pictogram unambiguous rather than to replace it. Directional arrows on green signs must be consistent along a route, because a single arrow pointing the wrong way at a junction undoes the whole run.
Fire signage uk premises use, in one place
Four categories cover almost everything a building displays. Green, a rectangle with a white pictogram, for escape and safe condition: the running figure and arrow on a route, the final exit, the first aid point, the assembly point. Red for fire equipment: extinguishers, hose reels, call points, blankets. Blue, a circle, for a mandatory action: fire door keep shut, keep locked shut, automatic door keep clear. Yellow, a triangle, for a warning, which in fire terms is usually a specific hazard rather than fire itself. Everything else on the wall is supplementary written information, the fire action notice among it, and it sits beside the four rather than inside them. The shape carries the category before anybody reads a word, which is the whole point of the system and the reason a building's own invented designs are a bad idea.
Other questions people ask
Is fire equipment signage green or red?
Red, rectangular, with a white pictogram. Green rectangles are safe condition signs for escape routes and exits.
Are photoluminescent signs required?
They are required where the sign must remain visible if the lighting fails and emergency lighting does not cover it. Many buildings use them alongside emergency lighting rather than instead of it.
Can a building use its own sign designs?
Not for the regulated categories. The shapes and colours are specified, and a bespoke design in the wrong shape does not meet the requirement however clear it looks in daylight.
What colour are fire equipment signs?
Red with a white pictogram. Red is the firefighting equipment family, which is why a red sign marks an extinguisher, a call point or a hose reel and never marks a way out.
What will a fire equipment sign indicate?
The presence and the position of firefighting equipment, and nothing about whether you should use it. A red sign with a white pictogram marks where an extinguisher, a hose reel, a call point or a fire blanket is, so that somebody who has decided to act can find it and somebody leaving can see it on the way past. It does not say the equipment is in date, it does not say which class of fire the unit is rated for, and it is not an instruction. The class rating is on the label of the unit itself.
What does a blue fire safety sign mean, and what about a mandatory fire safety signs set?
Blue is the mandatory category, meaning an action you must take, drawn as a white pictogram on a blue circle. In fire terms that is the family a building actually depends on: fire door keep shut, fire door keep locked shut, automatic fire door keep clear. They are the signs people most often remove during a refurbishment and never put back, and a fire door with no sign on an escape route is a finding an inspecting officer will write up. Blue is not green and not red: green means escape or safe condition and red means equipment, and the shape carries the category before anybody reads the words.