Use case
Require the action
Use where behaviour must be positively directed.
Mandatory signs for required action and PPE discipline
Use mandatory signs where the core message is what must be done, worn, or followed in the space.
Where mandatory signs fit
Mandatory signs sit where the work or movement pattern depends on a required action: wear PPE, follow procedure, keep a route or operational rule visible.
Which symbol applies follows from the required action. What the sign is made of follows from the site: the surface it mounts to, the cleaning it will meet, and how long it has to stay legible before it is replaced. Those are two separate questions and it is worth answering them separately.
Standards
What each standard covers here
Mandatory signs are the blue discs: ISO 3864-1 fixes the shape and the safety blue, and ISO 7010 registers the symbols inside them under M-codes. They state a required action rather than a hazard, so they are placed where the decision is made — at the entrance to the area, not inside it.
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
Local distribution
Need mandatory sign guidance for a site
Describe the required behaviour, PPE context, and whether the signs are part of a larger package.