The Sign Was a Letter: God gave Cain some sort of sign in Gen. 4:15. But what was it? The word for "sign" came to mean, in later Hebrew, a letter of the alphabet; not surprisingly, a number of interpreters concluded that God had put some letter or letters in Cain's body (sometimes, specifically, his forehead). Others explained that a supernatural sign was given to proclaim Cain's repentance to all, or that Cain was given a fearsome mark on his body-often, a pair of horns-to ward off potential attackers or given a dog to signal their arrival. . . . Note that another text speaks of a "mark" (on the forehead) for the wicked, as well as a contrary mark for the righteous:

For God's mark is on the righteous for salvation ... [but] those who act

lawlessly shall not escape the Lord's judgment.

They shall be overtaken by those experienced in war, for on their forehead

is the mark of destruction.

-Psalms of Solomon 15:6-9