About 3 years ago, I pitched a pair of shoes I made to a “big” shoe company – it used a POV device to spell words as you walk. I think it was a little too out there for the shoe company, but if you ever want to make your own, Dan on Instructables has a great how-to: “The Dance Messenger – Fun persistence of vision toy. Attach it to your shoe and write messages or patterns while you walk, run or dance!” Link.