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Two circular signs that mean opposite things. The pictogram inside is not what tells them apart — the colour and the fill are.
A red ring with a diagonal bar forbids the thing shown. A solid blue disc requires it. So the same pictogram of a person means 'do not enter' in red and 'this way only' in blue. If the circle is filled it is an instruction; if it is an outline with a bar through it, it is a prohibition.
Both are circular signs whose meaning is carried entirely by colour and fill: a red ring with a bar forbids, a solid blue disc requires.
Drawn from the visual attributes recorded for each symbol. Only traits the two records disagree about are listed.
| Trait | No smoking symbol | Mandatory action symbol |
|---|---|---|
| Built from | objects and circles | circles and people |
| Struck through | Crossed by a bar or line | Not struck through |
| Colour | red, white and black | blue and white |
| Symmetry | none | radial |
| No smoking symbol | Mandatory action symbol | |
|---|---|---|
| What it does | Forbids the depicted action | Requires the depicted action |
| How to tell them apart | Red outline ring with a diagonal bar | Solid blue disc, no bar |
| Colour of the pictogram | Black on white | White on blue |
| Typical example | A cigarette — no smoking here | Goggles — eye protection must be worn |
| Relationship (from Symbolwise's records) | Commonly confused with Mandatory action symbol — Both are circular signs whose meaning is carried entirely by colour and fill: a red ring with a bar forbids, a solid blue disc requires. | Commonly confused with No smoking symbol — Blue circles require an action and red circles forbid one; both are circular signs and the colour carries the entire distinction. |
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for what the symbol depicts, its shape-and-colour category, and any ISO reference number it reports. The standards themselves are paywalled and were not consulted, so nothing here is treated as an official definition.
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for what the symbol depicts, its shape-and-colour category, and any ISO reference number it reports. The standards themselves are paywalled and were not consulted, so nothing here is treated as an official definition.
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for what the symbol depicts, its shape-and-colour category, and any ISO reference number it reports. The standards themselves are paywalled and were not consulted, so nothing here is treated as an official definition.
A building's assembly point is a safe place to stand once you are outside. A ship's muster station is a staffed step in a procedure: you are counted against a roll, briefed, and if necessary allocated to a survival craft, which is why it has a letter or a number and appears on your cabin door card. Both are green, both show grouped figures, and both are called an assembly point in ordinary speech — and treating a muster station as somewhere merely to wait is the misunderstanding drills exist to correct.
The becquerel counts nuclear decays — one per second — and says nothing about harm. The sievert weights absorbed energy by the kind of radiation delivering it, and so estimates biological effect. A becquerel of one isotope and a becquerel of another can carry very different risk, which is exactly why exposure limits and medical doses are stated in sieverts and never in becquerels.
Count what is around the centre. Three solid blades radiating from a small disc is ionising radiation; three broken rings overlapping a central circle is biological hazard. They are the same size, the same colours and the same three-fold arrangement, which is why signage catalogues themselves get them wrong — and the responses could not be less alike. One calls for distance, shielding and time; the other for containment, disinfection and a disposal route.
The plain black flag excludes the competitor: their race is over. The black flag with an orange disc reports a mechanical problem that endangers others and sends the driver to the pits to have it fixed, after which they may rejoin. Both are shown with a number board, both are black, and confusing them costs a competitor a race they could have finished.