Sign and Seal in the New Covenant?

The Abrahamic and Mosaic covenants were made with different groups of people. The new covenant is the covenant of grace and it's made with all of God's elect. So why don't we call baptism both a sign and seal? No. Certainly it is a sign in that it signifies but it's not a seal under the new covenant. What is the seal? The Holy Spirit. And to call baptism a seal is to in some ways undermine the place of the indwelling of the Holy Spirit and life of the believer.