From the Foursquare site: Check in and shout “Go Packers!” or “Go Steelers!” to unlock your NFL team badge. Then head over to NFLShop.com to redeem your 20% discount code on select merchandise. Code expires 3/7/11.
Mashable article: Foursquare’s Super Bowl Campaign to Test Badge Redemption Codes
Huffington Post article: Foursquare’s ‘Super Bowl Sunday’ Venue Passes 70,000 Check-Ins