In biblical theology, a "sign of covenant relationship" refers to a physical or symbolic act, object, or event that signifies the establishment or renewal of a covenant between God and His people. These signs serve as tangible reminders of God's promises and the obligations of the covenant parties. Throughout the Bible, several key signs of covenant relationships are highlighted, each with its own significance and context.

1. The Rainbow (Genesis 9:12-17):
The rainbow is the sign of the covenant God made with Noah after the flood. God promised never to destroy the earth with a flood again, and the rainbow serves as a reminder of this promise. Genesis 9:13-15 states, "I have set My rainbow in the clouds, and it will be a sign of the covenant between Me and the earth. Whenever I form clouds over the earth and the rainbow appears in the clouds, I will remember My covenant between Me and you and all living creatures of every kind."

2. Circumcision (Genesis 17:9-14):
Circumcision is the sign of the covenant between God and Abraham, marking the physical and spiritual distinction of Abraham's descendants. Genesis 17:11 records God's command: "You are to circumcise the flesh of your foreskin, and this will be a sign of the covenant between Me and you." This act was to be performed on every male descendant of Abraham as a perpetual sign of their covenant relationship with God.

3. The Sabbath (Exodus 31:12-17):
The Sabbath is a sign of the covenant between God and the Israelites, symbolizing rest and sanctification. Exodus 31:16-17 states, "The Israelites must keep the Sabbath, celebrating it as a permanent covenant for the generations to come. It is a sign between Me and the Israelites forever; for in six days the LORD made the heavens and the earth, but on the seventh day He rested and was refreshed."

4. The Blood of the Covenant (Exodus 24:6-8):
The blood of sacrificial animals served as a sign of the covenant at Mount Sinai, where Moses sprinkled it on the altar and the people. Exodus 24:8 says, "So Moses took the blood, sprinkled it on the people, and said, 'This is the blood of the covenant that the LORD has made with you in accordance with all these words.'"

5. The Passover (Exodus 12:13):
The Passover lamb's blood, applied to the doorposts of the Israelites' homes, was a sign of God's covenant protection during the final plague in Egypt. Exodus 12:13 declares, "The blood on the houses where you are staying will distinguish them; when I see the blood, I will pass over you. No plague will fall on you to destroy you when I strike the land of Egypt."

6. The New Covenant (Jeremiah 31:31-34; Luke 22:20):
The New Covenant, prophesied by Jeremiah and instituted by Jesus, is marked by the internalization of God's law and the indwelling of the Holy Spirit. In Luke 22:20 , during the Last Supper, Jesus says, "This cup is the new covenant in My blood, which is poured out for you." This sign signifies the forgiveness of sins and the establishment of a new relationship between God and humanity through Christ.

Each of these signs serves as a profound reminder of God's faithfulness and the responsibilities of His people within the covenant relationship. They are integral to understanding the unfolding narrative of redemption throughout the Scriptures.