See the Scriptures I refer to above.
The Sabbath was most certainly an identifying sign of the Old Covenant, as was circumcision. Both identified a person as a member of the Old Covenant. Circumcision was the one-time entry sign, and Sabbath was the continuing, "remembrance" sign.
Let me clarify so there's no confusion (and this is why I made a distinction between terms in my post). My emphasis is on the words "Old" and "Covenant". The Sabbath is not sign of the "Old Covenant" (between God and Israel), but
a sign of who God's people are and to identify who our God is.
Ezekiel 20:19-20
'I am Yah your God; walk in My statutes and keep My ordinances and observe them. 20' Sanctify My Sabbaths; and they shall be a sign between Me and you, that you may know that I am Yah your God.'
Note this verse. He says The sabbath is a sign that we may know that he is "Yah" our God.
Remember that the many nations of the world served many gods with many names. And even today, notice how many religions call their deity the same name/title ("god"). But *our* Father's intention was to set himself apart as the one true God, as well as set apart those who profess to follow and believe in him. The Sabbath is that sign of separation; the true Hebraic meaning of the word Kodesh ("Set apart", "Holy"). This is why the sabbath was established as a sign LONG before our Father entered into a covenant with Israel...as far back as the 7th day of Creation (in Genesis).
This is specifically the reason why the Sabbath is the only commandment that (as you point out) has no moral implication. It's because it's the one specifically meant to show
from whose crew you rep (lol). Yah Almighty's...as he takes us back in memorial to the very day he sanctified the 7th and rested from his work. Only he did that. No other false god did that.
Next, circumcision wasn't a sign of the covenant between "God and Israel". It was a sign of the covenant between "God and Abraham". Completely different covenant than the one made with God and Israel.
The Covenant between God and Abraham was regarding
"Abraham's promised seed and the land God promised him". Meanwhile, the Covenant between God and Israel was as follows:
"
If you will obey my commandments I will makes you a nation of Priests...my unique treasure on the earth."
These are not the same covenants labeled "The Old Covenant"...but they have and do play a part together since Israel was of Abraham's descendants. God honored his promise to Abraham when he guided Israel to their promised land. But then he made another covenant with them so they would be his priests to the world.
In his (then) new agreement with Israel, he emphasized that he would circumcise their hearts to love him with every ounce of their being. Then later on Christ said the greatest commandment is (in fact) to love God with every once of one's being, which directly ties it to the Father's "circumcision of heart". Thus to love God with one's everything is to be circumcised by God. This is why I say and Paul says circumcision still exists (just spiritual).
In addition, the word Law most certainly does refer to the Old Covenant in some places.
As I note in the other answers, the Old Covenant was between God and Israel. We are not parties to that covenant. The Sabbath was the sign of that covenant, along with circumcision. The Old Covenant was only in place until Christ came. See Galatians 3. It no longer applies to anyone now. And neither does the Sabbath because it was part of that covenant. The Sabbath is not a moral absolute like the other 9 commandments. The New Covenant involves much higher demands including loving others like Christ loved them.
I agree. The covenant (which I will coin the "nation of priests" covenant) was between God and Israel and no one but Israel is a party to that covenant. However, the covenant wasn't made *until* Christ came, rather Christ re-instituted that covenant through new testament (i.e. testimony/witness) in his blood, making the "old" covenant "new" (as in "
Brand spanking new") and everlasting (as in "forever and ever").
You see prior to Christ, notice as soon as Israel sinned and broke the covenant it was never actually fulfilled. Israel was never a nation of priests to anyone. They never spread the message of God to the nations of the earth. Everything was on pause. Israel was in a black hole regarding that promise until that nation could be restored. God doesn't go back on his promise; Israel was supposed to be the nation of Priests to take his name to the world...no other nation.
So with Christ as the facilitator of the restoration and with his rightful claim as King,
Christ IS Israel. And anyone who is grafted into Christ is part of the same body. As Paul says there is one body. And as the Book of Numbers says there is
one law for the native and stranger grafted in (Num 15:16).
More to the point, notice that the covenant promise that God makes in Exodus (for Israel to be a nation of priests), is the *same exact* promise that Peter declares to the reader in the new testament, which is the same exact promise fulfilled in the book of Revelation at the end of days for those who "overcome".
Exodus 19:5-6
"'Now then, if you will indeed obey My voice and keep My covenant, then you shall be My own possession among all the peoples, for all the earth is Mine; you will be (future tense) for me a kingdom of priests and a holy nation.' These are the words you are to speak to the Israelites."
1 Peter 2:9
"But you are (present tense) a chosen people, a royal priesthood, a holy nation, God's special possession, that you may declare the praises of him who called you out of darkness into his wonderful light."
Revelation 1:6
"and has made us (past tense) to be a kingdom and priests to serve his God and Father--to him be glory and power for ever and ever! Amen."
It's the same covenant, past, present and future.
When the ignorant and unstable say that Jesus Christ changed God's law (which he didn't), they're actually accusing him of the very thing his enemy will do. It's amazing how discieved the world is. 
