The Heroes of the Storm Pennant is a pennant available in Diablo III for players who reach at least level 12 in Heroes of the Storm. It comes with a similarly-themed portrait frame. Both rewards are unlocked immediately if the account has Diablo III game.
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.
You are a hero. Of the storm.