Overwatch Twitter account teases something, possibly new event or hero

The Overwatch Twitter account has posted a teaser of... something. It depicts what appears to be an alleyway adorned with posters and other graffiti expressing both pro- and anti-Omnic sentiment. There's also a Lúcio concert promotion, a poster depicting Horizon Lunar Colony, and a few paintings of several animals in space suits, including a monkey and a dog. 

That last bit is probably the most interesting, as previous in-universe teasers mentioned several other animal test subjects at Horizon Lunar Colony (where the scientist/gorilla/tank Winston was created), including a subject referred to as "Hammond." It's possible that this teaser is the first hint at a new hero or an upcoming event. Knowing how Blizzard likes to tease these things out in increasing detail, we'll probably know more in the coming days.