The foursquare Starbucks badge appears to only be available this week and can be unlocked by following Starbucks and checking in to one of their shops.
Below is the text that appears when you unlock the Tribute Badge:
Thank you. We started in 1971 and are turning 40. You’ve earned this badge and a chance to win a $40 Starbucks card. Sweepstakes ends 3/12/11. For complete details: http://sbux.co/TributeBadgeRules