Dive summary: 

• The Spanish non-profit organization Aid to Children and Adolescents has released a billboard designed to show adults one image and another image with an abuse hotline to children. 
• The billboard uses a  precisely serrated surface, a Lenticular lens, that reflects light differently to those looking from above and below a specified height; those below 4'5" tall will see a hotline number with the message “If somebody hurts you, call us and we’ll help you."
• The Lenticular lens trick has been used for decades by toy manufacturers and other ad campaigns.

From the article: 

"In the future, we could imagine more advanced warning systems. IBM is reportedly developing ads that remotely targets a user’s individual interests, based on radio frequency-enabled cards that they expect consumers will carry with them. Similarly, malls can now track users’ cell phone signal as they travel from store to store for marketing data. It’s not hard to imagine a billboard beaming abuse-notification messages to a child’s cell phone, or, more discretely, to a technology like Google Glass."