Search your library for three creature cards and reveal them. If you reveal three cards with different names, choose one of them at random and put that card into your hand. Shuffle the rest into your library.
Gruul clanfolk obey few rules, but all feel bound to answer the call of the horn.
Official Rulings for Signal the Clans
1/24/2013 : If you don't reveal three creature cards with different names, you'll simply shuffle your library (including any cards you revealed).
1/24/2013 : All players will see the card you put into your hand, if any.