A visible marker God has appointed as the public token of a specific covenant. Scripture names several. The rainbow (Gen 9:12-17) signs the Noahic covenant of God's pledge never again to destroy the earth by flood. Circumcision (Gen 17:11) signs the Abrahamic covenant of God's pledge to be God to Abraham and his seed, marked in the flesh. The Sabbath (Ex 31:13-17) signs the Mosaic covenant between God and Israel as the people set apart in time. Baptism and the Lord's Supper sign the New Covenant ratified in Christ's blood (Matt 26:28; 28:19; 1 Cor 11:25). Each sign is more than memorial — it is God's self-pledge made visible. To despise the sign is to despise the covenant; to receive the sign rightly is to bind oneself in faith to the God who has signed Himself first.