List of Foursquare Badges – Wikipedia, the free encyclopedia

The Foursquare staff are very secretive about how to unlock many badges. There are a handful of introductory badges that are earned as milestones in usage. Some badges are tied to venue “tags” and the badge earned depends on the tags applied to the venue. Other badges may be specific to a city, venue, event, or date. Some badges utilize identical icons, but are earned differently. There are a few known badges that are named similarly, but applied differently, specifically Far Far Away, Trifecta and I’m on a Boat.
(Link: List of Foursquare Badges – Wikipedia, the free encyclopedia)