How does Karkat have a sign if his ancestor is the signless???

“After [The Signless’s] execution, the body was burned leaving only his irons. They cooled in the ash, as if his anger itself was subsiding, and his followers appropriated their shapes in defiance of the Highbloods. The symbols became the sign of the Signless, always shown as colorless as the cold iron, to conceal the stigma of his hue”