Recusant's Sigil

The Recusant's Sigil (異端の印) is a symbol designed by Xehanort to represent the rejection of a Nobody from his original persona. It is incorporated into the new names of each of the original members of Organization XIII, and it is derived from Xehanort's sleeping memories of the χ-blade.

In order for Xehanort to track his movements in the Sleeping Worlds, Sora was marked with the Recusant's Sigil, which took on the physical form of a silver "X" on his shirt.