Well, seeing how the URL is eu.battle.net/sc2/en/blackstone
I'll go ahead and point out that the URL states what it's going to be for.
If you still can't grasp what SC2 stands for. It's an abbreviation for Star Craft 2.
Vass23 posted a picture of Blizzards Product Slate, which shows Star Craft 2: Phoenix
Which leads us to the logo of Project Blackstone - A Phoenix