Genesis 4:15

15And the Lord said to him, “4:15 Some ancient versions read, “Not so!”Therefore, whoever kills Cain, a sevenfold vengeance [that is, punishment seven times worse] shall be taken on him [by Me].” And the Lord set a [protective] 4:15 Many commentators believe this sign not to have been like a brand on the forehead, but something awesome about Cain’s appearance that made people dread and avoid him. In the Talmud, the rabbis suggested several possibilities, including leprosy, boils, or a horn that grew out of Cain. But it was also suggested that Cain was given a pet dog to serve as a protective sign.mark (sign) on Cain, so that no one who found (met) him would kill him. [Gen 4:24]