A Canadian company Mirage Motion Media came up with a technology that creates an illusion of motion for static billboards.
Here's what they say: "Mirage motion panels work thanks to a psychological phenomenon known as persistence of vision. When your specially produced motion prints are backlit and viewed through a series of thin vertical apertures, viewers perceive uninterrupted moving pictures. It's the same effect that makes the lines between celluloid frames disappear when you watch a film in a theatre." A bit like the subway tunnel ads.