For the event itself, see BlizzCon.
The BlizzCon 2015 (or BlizzCon Pennant) is a pennant available in Diablo III for players who have participated in BlizzCon 2015.
It comes with a similarly-themed portrait frame and a Murkgoblin non-combat pet.
When obtained, it can be added to Wardrobe. Only one pennant can be used at a time. If equipped, it will be visible even in character selection screen.
Only the few, the proud, the hardest of the hardcore are worthy of flying with those colors.
Curious how you'd look as a Murkgoblin's tasty snack? Wonder no more! (portrait)