If he's the Signless, then who is the proper Cancer troll?
From what I understand, the Signless and the Sufferer are the same person. The Sufferer is Karkat's ancestor, and was one of the previous session's players. However, after failing his revolution, the Empress had his sign and all references to it banned. His sign was forgotten, as if it never existed, so he was signless.
I was just thinking about how Karkat/Karkancestor chose his sign. His blood was a mutant colour, so he probably didn't have any signs for it. I wonder if he chose one for one of the normal blood colours, or made one himself. Or was it Karkat choosing it because his ancestor had it, and his ancestor chose it because his ancestor-from-another-timeline had it, like some sort of time paradoxes.