We've always known that there are more characters and maps coming to Overwatch. Blizzard has even said that they've hidden a few hints about the characters both in the game and in their marketing material. This hint, however, isn't exactly subtle.
Overwatch's official Twitter account decided to post this image:
Our first guess is that this is the mysterious Sombra's weapon. The supportive sniper has been teased in both videos, character dialogue and maps, and now it seems that she's about to make her entry.