'Sign' in the Bible

Then Yahweh said to him, "Therefore, whoever kills Cain will be avenged sevenfold." Then Yahweh put a sign on Cain so that whoever found him would not kill him.

And God said, "This [is] the sign of the covenant that I am making between me and you, and between every living creature that [is] with you for future generations.

My bow I have set in the clouds, and it shall be for a sign of [the] covenant between me and between the earth.

And God said to Noah, "This [is] the sign of the covenant which I am establishing between me and all flesh that [is] upon the earth.

And you shall circumcise the flesh of your foreskin, and it shall be a sign of the covenant between me and you.