The Sigma Austria Facebook page is teasing a new lens to be unveiled on February 23, 2016. By the shape of the outline, it looks like they may be teasing a telephoto zoom lens faster than f/2.8.
If you have more information than that, please let us know.
The world is waiting for Sigma to release an 85mm f/1.4 Art series lens, and it looks like we'll have to wait a little while longer.
Thanks Alexander