Yes, the mark..... it seems pretty lame to me. I guess it could be equated with the mark of Cain, the mark of a murderer. It can't be there to warn others about her violent tendencies as was pointed out...who is gonna see it there? I think it is a mark that is intended to illicit a reaction from Jack. It offers him proof that Juliet is really on the outs with her people. It gives them another thing in common, since he is also marked with a tattoo. Now he feels like both of them are misunderstood, marked, being held against their will by Ben and the others, and both of them have falsely been promised their freedom. All of this empathy for Juliet gives Ben and the others more power over him. I would like to know if the symbol has any relevance at all or if it is just as random as it seems.