An old saying tells us it does no good to beat a dead horse, so, if you are aware that this story about Cain and Able cannot be factual, pardoning me for making that point one more time. Although the story presents Cain as the first man born in this world, and he is described as a tiller of the soil, this does not fit in with the historical fact that while humans have been on this earth for hundreds of thousands of years, there is no evidence of their taking up farming more than twelve thousand years ago. The same is true of tending domesticated animals, the occupation of Cain’s brother Abel.
Cain is described as being crestfallen at his sacrifice not being accepted. That is an expression we no longer use. Your crest is your forehead. You are crestfallen when your forehead tries dropping below your eyebrows. Try it! You will find it puts you in the mood for jealous brooding.
The slaughtered Abel’s blood is said to have cried out from the ground. That understanding is found elsewhere in the Bible. There are also stories of murderers scraping dirt over the spilled blood to prevent it from crying out for vengeance.
When the story has Cain, supposedly the first man born into this world, complaining that anyone who sees him would kill him the story itself is telling us not to believe it. What it does factually tell us is that there was a time when any unattached stranger would have been such a menace that the safest thing would be to kill him.
The story is letting us know that in those days wandering tribes protected each wandering member by giving him a distinctive tattoo that guaranteed that his tribe would take two or more lives from any tribe that killed one of theirs. So, the mark of Cain did not advertize Cain as a murderer. What it did was protect him by the Lord promising to take seven lives from any group that touched Cain.