Safety signs are a system before they are pictures. Shape and colour classify a sign before the pictogram inside it says anything: a green square marks a safe condition, a red circle with a diagonal bar forbids, a red square locates firefighting equipment, a yellow triangle warns, a blue circle requires. Grouped for that reason — learning the grammar lets a reader classify a sign they have never seen, which is worth more than knowing any single pictogram. The distinction most often reversed is red: on a square it means fire equipment is here, not that danger is here.
A white running figure heading through a door on green, marking the way out.
Four white figures around a point on green, marking where to gather.
A white cross on green, marking first aid provision.
A heart with a lightning stroke on green, marking an AED.
A white extinguisher on red, marking firefighting equipment.
A lit cigarette in a red circle with a diagonal bar.
A white pictogram on a solid blue circle, requiring an action.
A black exclamation mark in a yellow triangle.
A black lightning arrow in a yellow triangle, warning of electrical danger.