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.
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.
They are alternatives, not a pair. The double square means the appliance is protected by double or reinforced insulation and needs no earth connection, which is why it can legitimately have a two-pin plug. The earth symbol marks a terminal that must be connected, because that appliance relies on earthing instead.
Shape and setting decide it. A yellow triangle on a wall or a machine is the general safety warning sign: a hazard is present, unspecified, so read the text beneath it. A red-bordered diamond on a product label is the GHS pictogram, which is not vague at all — it stands for a defined set of chemical hazard classes such as skin or eye irritation.