Also it is THE ONLY thing in the Scriptures called "the mark of Yahweh"
*Sign is Word #226, Hebrew Dictionary, Strong's Exhaustive Concordance, meaning mark, token, sign, consent, flag, evidence of consent.
Exodus 31:13-17, "Speak also to the children of Israyl, saying; Surely My Sabbaths you shall keep, for they are a *sign between Me and you throughout your generations, that you may know that I am Yahweh Who sanctifies you, and makes you holy"....16-17, "Therefore the children of Israyl shall keep the Sabbath, to observe the Sabbath throughout their generations as a perpetual covenant. It is a sign between Me and the children of Israyl forever, for in six days Yahweh made the heavens and the earth, and on the Seventh Day He rested and was refreshed."
Ezekiel 20:12, "Moreover, I also gave them My Sabbaths, to be a *sign between Me and them, that they might know that I am Yahweh Who sanctifies them."
Romans 9:6-8, "However, it is not as though Yahweh's plan had failed. For it is not everyone who is a descendant of Israyl who belongs to Israyl. Nor, just because they are his descendants, are they all Abraham's children; but: In Isaac will your seed be called. That is, it is not those who are the children of the flesh who are Yahweh's children; but it is the children of the promise who are regarded as Abraham's seed."