The word “mark” in Genesis 4:15 in the King James Version of the Bible is a translation of the Hebrew word “owth.” According to “Strong’s Exhaustive Concordance of the Bible“, the Hebrew word “owth” may be rendered “mark,” or “signal, flag, monument, sign, or beacon.”
The “owth” — mark or sign — that God made for Cain could have been something to carry on his person, perhaps around his neck — from which the ancient and modern custom of wearing a charm or talisman for protection may be derived. Is it not possible that Cain or his descendants may have begun to look upon this sign — which may have been in the form of a CROSS — as a “good luck” charm and turned it into an item of idolatrous worship? (Compare Num. 21:4-9 with II Kings 18:4 for a similar example.) The various forms of the cross are of pagan origin and go back to earliest antiquity.
The Hebrew word “owth” could also indicate even a boundary marker that God set up to separate or segregate Cain and his descendants from the rest of mankind. Genesis 4:12 shows that God banished Cain to the land of Nod — meaning land of “wandering” — east of Eden or Palestine.
The “Jewish Publication Society” translation renders Genesis 4:15, “And the Lord said unto him [Cain]: ‘Therefore whosoever slayeth Cain, vengeance shall be taken on him sevenfold.’ And the Lord set a SIGN FOR Cain, lest any finding him should smite him.” The original Hebrew conveys both meanings — a mark on the person of Cain, or a sign set up for him to segregate him from others.
Some have thought that Cain’s mark involved skin color. Cain’s mark was NOT the changing of his skin color as some suppose. Cain, in accordance with certain West African traditions, may well have been dark, but his sin was a matter of character, not of heredity.
God created ALL races — white, yellow and black, to serve and glorify Him with their own particular abilities. Racial differences are not due to the “mark of Cain.” God originally planned that humanity be divided into various races so that they might learn to live and work together in their own respective heritages around the world.
Source: Plain Truth, 1967