I agree with Kostas on page 3. I believe it is Xion or a matter of her/him. Doesn't anyone remember what Xion is in 358/2 days? *Ding ding ding* A puppet! And what did Xion look like to everyone for being a puppet? *Ding ding ding* Someone or something totally different! Everyone up to this point could have possibly assumed Vanitas was a guy(Besides MX), becuase they didn't know what his face looked like, until the scene in the new trailer.
And if you were to look at Sir Adamus's sig, that isn't a fan drawing of Xion.
Yes some people are going to say, that the hair over the eyebrow is longer in the sig than the scene. But time passes, and or the hair could have been pushed up by the helmet. But there's no mistaking it, Vanitas could be another form of a past version of Xion.
Edit: I just noticed this but in the same pic, there's another part of Vanitas helmet coming off on the right. And it shows the hair curving to the right and down, with no strands of hair coming down over the right side of the forehead. And if you were to find that same position on Sora, Roxas, Ven, and Xion on Sir Adamus's sig, Xion is the only one that fits the discription.