When designing and placing warning signs, follow these basic criteria:
- Only use warning signs when and where needed
- Make sure that all warning signs are clearly understandable and that they stand out from the background in order to attract attention
- Ensure that warning signs are durable
- All warning signs should contain clear and realistic instructions about action
- Preferably, the sign should indicate what would happen if the warning is not heeded
Warning should not be present when the hazard is absent, otherwise people will soon learn that it is not necessarily dangerous in that area, devote what the signs indicate. They will then look for further confirmatory evidence that something really is a problem before taking confirmatory action. The philosophy of 'if in doubt, put up a warning sign' is counterproductive unless an organization is prepared to go to great lengths in enforcing it, even in the face of the lack of need for the precaution at some times.
If an alarm goes off and there proves to have been no danger, there will be a small, but perhaps significant, loss of confidence in it. If false alarms exceed true ones, the first hypothesis of an individual will be be that it is a false alarm.