Digital coupons are a high-growth area for online marketers; Foursquare is as well. The former, though, has a clear path to ROI for both buyers and sellers. Until recently, the same couldn’t have been said about the wildly popular game. Enter coupons targeted by geolocation - which is showing signs of becoming a robust  monetization strategy for Foursquare.

The key has been the formal alliances the company has been striking with brands and stores - alliances that are "turning into real money for an app that many people believed was pointless when it started," says VentureBeat. According to Foursquare CEO Dennis Crowley more and more stores, restaurants and brands are joining the company's new digital coupon program. Essentially it works with the store or restaurant posting stickers in windows offering the coupons to Foursquare users. One example is AJ Bombers, a hamburger restaurant in Milwaukee, which reported a 30% jump in sales after it posted Foursquare stickers in its windows, according to VentureBeat. Another example is JFK airport where patrons can get a free taxi ride if they become mayor at the taxi stand.

Other digital coupon companies are riding this trend: Yowza, an iPhone and iTouch app that uses GPS technology to find the user's location and deliver digital coupons, targeted several Austin-based based companies during SXSW to negotiate special coupons for their app, according to the Wall Street Journal. These included the indie record store Waterloo Records, the Alamo Drafthouse movie theater, Frank, a hot dog restaurant, and clothing stores Secret Oktober and Gallery D.