A Spanish charity has revealed a unique ad poster that aims to help abused children by revealing a helpline number only to them. Aid to Children and Adolescents at Risk Foundation (ANAR) has designed outdoor posters that reveals a warning message to adults but displays a secret message only for children.

The campaign, created by ad agency Grey Spain, hopes to empower abused children by secretly giving them a number to call for help without alerting their abuser even if their abuser happens to be standing next to them.

ANAR was concerned that if the anti-abuse phone number is both visible to children and adults, the adults may possible dissuade their child from seeking help.

The ad agency has used a lenticular printing technique, which is typically used in novelty postcards and kids’ stationery products. The technology produces printed images with an illusion of depth, allowing the display of different messages when viewed from different angles.

From an adult’s point of view, or anyone taller than 4’5”, the ad shows an innocent poster with a boy’s picture and an awareness message that reads: “Sometimes, child abuse is only visible to the child suffering it.”

Children with a height of 1.35 metres, which is the average height for kids 10 years old and below, will be able to see the boy in the poster with bruises, with the message, “If somebody hurts you, phone us and we’ll help you,” alongside the phone number 116 111, the European child helpline number.

From an adult’s point of view, or anyone taller than 4.3 feet, the ad shows a warning message that reads: “Sometimes, child abuse is only visible to the child suffering it.”

“It is a message exclusively for them, hidden from adults’ eyes,” Grey Spain said.

“It uses a lenticular to combine two images, and we have calculated an area visible only to children under ten – and a warning for adults.”

The ad agency explains how the poster works in a YouTube video titled “Only for Children.”