Ads that let you check in at your favorite billboard - San Jose Mercury News

Ads that let you check in at your favorite billboard - San Jose Mercury News: "Foursquare, a rapidly growing social network, lets people use their mobile phones to announce their location to friends. When they arrive at a restaurant, bar or another site, they 'check in' and can broadcast their whereabouts through other social networking sites like Facebook and Twitter.

The Earthjustice campaign appears to be among the first to let people check in at a physical billboard, a tactic that has proved successful for the firm and could be attractive to other advertisers, according to industry analysts and Foursquare executives."