Believers need not worry about signs of the covenant. They are good to know about and understand but not essential.
Jesus Christ baptizes us with the Holy Spirit into His body at the time of regeneration/salvation. That is when and how we receive the sign of the New Covenant.
Since God puts no conditions on us in that we have to meet that covenant is everlasting. In fact it existed in the mind of God before the world began.
Also, since God put no conditions on Abraham when He made His covenant with him and his descendants and calls it an "everlasting covenant" Gen. 17:7, 10-11 I do not think that covenant has or can cease.
While Judaism is a false religion there remains within the seed of Abraham a remnant that knows the true Messiah. According to Romans 9:27, 11:1, 5 that remnant exists and will be saved according to "the election of grace."