Check out how Wargrave describes the way that he kills himself: “The third is symbolical. The manner of my death marking me on the forehead. The brand of Cain” (E.197).
The mark on Wargrave’s forehead is symbolic because it hearkens back to Hebrew Bible’s story of Cain and Abel. In the story, Cain kills his brother Abel, and then God slaps a mark on his face so everyone will know it. In the same-but-different-way, Wargrave is marking himself as the person who has killed all the other inhabitants of Soldier Island.
Let’s expand on that. The similarities are pretty obvious: murderers get marked. Great. But the differences are where things really get interesting. First, Wargrave is marking himself. Does that mean he thinks he’s like God? Probably. As Philip Lombard remarks:
“But to begin with, he’s an old man and he’s been presiding over courts of law for years. That is to say, he’s played God Almighty for a good many months every year. That must go to a man’s head eventually. He gets to see himself as all powerful, as holding the power of life and earth—and it’s possible that his brain might snap and he might want to go one step farther and be Executioner and Judge Extraordinary.” (10.32)
But does it mean he admits guilt?
Maybe not. Even though Wargrave knows that he’s committed some crimes he’s still proud of himself. In a way, the mark that he gives himself actually signifies that he’s done something great.