Earlier today, Microsoft apparently slipped up and showed Metal Gear Rising's box art on the Xbox Live Marketplace. It's gone now, but the internet, she never forgets.
If this is indeed what happened, it's...yeah, it's a game cover! One that may change, since the game is nowhere near release! Metal Gear fans will be thrilled, though, no doubt poring over every pixel searching for clues as to what's actually going to happen in the game.
All I can see is that Raiden is sparky. Oh, and that the most talented people at Kojima Productions may well work in logo design.