The biblical covenant sign God placed in the sky after Noah’s Flood was a rainbow.
In Genesis 9, God establishes a covenant with Noah, his descendants, and every living creature that the earth will not again be destroyed by a flood of that kind. The rainbow is presented as the sign of this covenant.
Genesis describes the rainbow as appearing in the clouds. Whenever it is seen, the text says, God will remember the everlasting covenant between God and all living creatures on earth.
The passage makes the rainbow more than a weather phenomenon within the story: it is a visible reminder of a divine promise. Biblical translations may vary slightly in phrasing, but “rainbow” is the standard English term used for the covenant sign.