If you fire up the Destiny beta on Saturday, regardless of platform, you will be given a special reward for the full version of the game when it releases later this year.

All you need to do is log into the beta on Saturday, June 26 at 2PM (PT). That's it. The message sent to players today does not specify what that reward might be, only that it will be for the full retail release of the game. With any luck, the reward will be the actual Peter Dinklage showing up at your house to give you a reading of the famous Moon Wizard line.