User blog comment:Fusedtwilight/Possible Season 11 Plots/@comment-78.145.128.117-20150525133803/@comment-25529791-20150525193809

Okay, my logic may be arguable but for the sake of discussion, I'll bring it up.

1) Maybe the Mark didn't work like it's supposed to (we're assuming that Lucifer has it) because Lucifer's in the Cage? I mean, Cain had the Mark all along so Lucifer's freedom didn't matter all that much.

2) Since Lucifer is an Archangel and needs to take a vessel, maybe the Mark is branded into his soul/grace? Because he needs to keep changing hosts right, so I guess it's not necessary that the Mark be shown on each vessel.

2.5) Maybe the creators didn't show the Mark because back then, they hadn't thought of this whole Darkness thing and it could be counted as an error. Or it could be that we never saw the places on their arms where the Mark is supposed to be?

Yeah, I know the last one is feeble, I don't really believe it that much either. I just brought it up for the sake of discussion.