What's the Mark of Cain?

The Answer:

It's amazing how many people don't at least know that this expression derives from The Bible's Book of Genesis. Less surprising is that even more people wrongly assume that this mark was to call attention to Cain's crime of fratricide.

Cain felt that God was showing favoritism to his brother, Abel, and responded by whacking his sibling. The Lord punished Cain by casting him out of paradise and Cain settled east of Eden (another question answered?). But Cain was afraid that he, in turn, would be killed by someone else for having committed the crime, so God put a protective sign on him, The Mark of Cain. But this protective mark also represented the worst kind of punishment. Cain would have to live out his natural lifetime contemplating the horror of what he did. He would thus punish himself. So if someone threatens you with the Mark of Cain, plea-bargain.