A few decades ago, billboards were an advertising powerhouse. Place your ad by a major highway, and everyone sees it as they go by. In the 21st century, you can reach more people over a wider area ...

To onlookers with standard color vision, the billboard looks like a bit like a magic eye picture made up of green dots. But no matter how long they look at it, the hidden message won't appear ...

David Cline's billboard, on the way to West Philadelphia and near 34th Street, notes that he can cook and has a cat and "normal hobbies." (David Cline) ...