Use case
Stop the action
Use where preventing a behaviour is the key objective.
Prohibition signs for clear behavioural boundaries
Use prohibition signs where the message must stop a specific action before it becomes a safety or operational problem.
Where prohibition signs fit
Prohibition signs are used where the message must be unambiguous: do not enter, do not smoke, do not operate, do not proceed. This family fits when the primary job is to stop a specific action.
Which symbol applies follows from the action being stopped. What the sign is made of follows from the site: the surface it mounts to, the cleaning it will meet, and whether the boundary still has to be readable when the lighting fails. Those are two separate questions and it is worth answering them separately.
Standards
What each standard covers here
Prohibition signs are the red circles with a diagonal bar: ISO 3864-1 fixes the shape and the safety red, and ISO 7010 registers the symbols inside them under P-codes. The bar is what makes the message negative, which is why the symbol underneath is never modified to carry the negation itself.
ISO 7010
The registered safety signs. Symbols are reproduced as registered, not redrawn.
ISO 3864-1
Safety colours, geometric shapes, and the relationship between viewing distance and sign size.
ISO 3864-3
The design rules a graphical symbol is drawn by, including one that is not in the register.
ISO 17398
Classification, performance and durability: material class, environment, service life and the test behind it.
Related families
Warning Signs
Use where the first job is hazard recognition rather than forbidding an action.
View categoryMandatory Signs
Use where the message must require a specific action rather than prohibit one.
View categoryLocal distribution
Need prohibition sign guidance for a site
Share the restricted action, the location, and whether the sign belongs to a wider standard-led package.