Gizmodo - This Ad Has a Secret Anti-Abuse Message That Only Kids Can See

Developed by the Grey Spain, this simple but effective Out of Home advertising uses a simple lenticular technology to achieve its campaign objective.

From Gizmodo -

In an effort to provide abused children with a safe way to reach out for help, a Spanish organization called the Aid to Children and Adolescents at Risk Foundation, or ANAR for short, created an ad that displays a different message for adults and children at the same time. The secret behind the ad's wizardry is a lenticular top layer, which shows different images at varying angles

Good Out of Home advertising is - simple, effective and thought provoking. Algorithm mix of location, media, creative, production techniques and execution.