'Sign' in the Bible

And the Lord said to him, “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] mark (sign) on Cain, so that no one who found (met) him would kill him.

I set My rainbow in the clouds, and it shall be a sign of a covenant between Me and the earth.

And God said to Noah, “This [rainbow] is the sign of the covenant (solemn pledge, binding agreement) which I have established between Me and all living things on the earth.”

And you shall be circumcised in the flesh of your foreskins, and it shall be the sign (symbol, memorial) of the covenant between Me and you.