Recusant's Sigil

"As your flesh bears the sigil, so your name shall be known as that...of a recusant."

—Xemnas to Sora, at the beginning of their battle.

The Recusant's Sigil (異端の印, Itan no shirushi, lit. "Mark of heresy") is a symbol created by Xehanort to represent a Nobody's rejection of their human form. The symbol itself is derived from Xehanort's sleeping memories of the χ-blade. Each of the members of the original Organization XIII had names that bore the Recusant's Sigil.

In order to track his movements in the Sleeping Worlds, Xehanort marked Sora with the Recusant's Sigil by placing a silver "X" on his shirt.