Icon Reward?

First off, I had no idea where to post this so it may very well be in the wrong board. Anyways, I just got a message on my client that said "Reward Unlocked". When I clicked it it popped up a message that said, "Thank You" and gave me an icon that I've never seen before. Does anyone know what it was for? I have no idea. Not that I mind a free icon, I'm just confused on what warranted it since I'm the only person I know who got one, and no one has any clue what it could be for. Thank you in advance.

Edit: If I knew how to change my icon on the boards instead of just the client I would put it on for reference. :/