Billboards are everywhere, so why not have them do something useful? That's the thinking behind IBM's new "Smarter Cities" campaign, which modifies the regular billboard shape to perform a secondary function. As shown in a promotional video created by the ad company responsible for the posters, a simple curve at the top or bottom of a billboard can create shelter or seating for passers by, while a ground-level protrusion can form a ramp to help people climb stairs.

The ads are supposed to spark people to join in with IBM's People For Smarter Cities initiative, which looks for citizens' ideas on how to make cities a better place to be in. Of course, the billboards are just a PR stunt, but after being viewed online by over 50,000 people in a matter of days, they're a highly effective stunt.