Most of the certifications dealing with hygiene in food industry requires handwashing signs, especially in toilets.
Ben Chapman, Barfblog, a blog dedicated to food hygiene, explains why such signs are useless.
Read the story (in English)
“Surprising information plays a fundamental role in the learning and adoption of new behaviors”
If you want workers to be compliant with handwashing, the best way is the example. Managers should wash their own hands regularly.
“Handwashing signs in restrooms don’t matter; washing hands matters.”