An image was posted over on Reddit's /r/wow today that shows some of the signage being put up outside the Anaheim Convention Center today. Stuff like this is pretty common for conventions, and Blizzard is just tweaking their design a bit, putting the games outside instead of indoors.
Zooming in, as many people have, reveals nothing of consequence, however. The WoW image is just a picture of an Orc (Edit: Yes, it's Thrall, who is an Orc). And while Orcs originate from from Draenor, it doesn't give any clue as to what the next expansion is. Orcs are all over WoW's media.
Blizzard handles all the new media and things by putting the material up before hand and covering them in black cloth. That's what they'll do this year, too -- so unless you're in the hall early, you won't know what it is. And on that note, no one gets in the hall early. The security there is insanely tight, there is no chance of getting in.
Still, it's interesting to see things moving forward.