This anti-abuse ad has a secret message. Can you see it?

It may be one of the most creative ad campaigns ever.

A Spanish organization called the Aid to Children and Adolescents at Risk Foundation has created an ad that has different messages for children, who may be abused, and adults at the same time.

Here is how it works: The billboard has a lenticular top layer meaning it shows different images at different angles. When an adult — anyone taller than 4’ 5” — looks at it, they only see the image of a sad child and the message: “Sometimes, child abuse is only visible to the child suffering it.”

But when a child — shorter than 4’ 5” — looks at the same ad, they see bruises on the boy’s face and a different message: “If somebody hurts you, phone us and we’ll help you.” The foundation’s phone number is on one side.

But even smart, revolutionary campaign doesn’t come without flaws.

For one, what if a child abuser is also short? He can see the message too, and he is forewarned, said one viewer on YouTube.

The video has been viewed almost 4 million times since it was posted about two weeks ago. 

Another viewer pointed out rather snarkily that children in the U.S. can’t read simple sentences until they are 6 to 8 years old.

Some have said that because this ad has gone viral, it’s only a matter of time that toy companies adopt the lenticular technique for more profits. 

Raveena Aulakh is the Star's environment reporter. She is intrigued by climate change and its impact, now and long-term, and wildlife. Follow her on Twitter @raveenaaulakh