NOTE: there is a shiny silver "A" on the side of the lens in the picture, meaning this is their "Art" line of lenses - the same breed as the 35/1.4 that has blown away many many people.
It's also proof positive that the pic is a fake. IIRC the Art designation is for lenses with a large maximum aperture.
It's not a fake unless someone has hacked Sigma's website as part of an elaborate joke.
I know because I stumbled onto Sigma's page on this
It says "Planned date available: September 2013 for Canon (to be determined for Sigma, Sony, Nikon, Pentax)".
(First-time poster here.)