This is brilliant. The organization Aid to Children and Adolescents has created poster ads for public places that displays an abuse hotline number that only people shorter than 4’5″ can see, TechCrunch reports:
The secret is a precisely serrated surface, a Lenticular lens, that reflects light differently to those looking from above and below a specified height. Shorter people (children) see the following message on a street sign: “If somebody hurts you, phone us and we’ll help you.”
Adults see, “Sometimes, child abuse is only visible to the child suffering it.” The ad is especially designed for children who may be traveling with their abuser.