1. it was a sign to Israel. Not the church
The Sabbath was indeed a sign to Israel. As scripture says, a sign of God's deliverance from Egypt/slavery/sin, and a sign that their sanctification was solely in the hands of God.
Yet Jesus said that the Sabbath was made for mankind.
KJV Mark 2:27
27 And he said unto them, The sabbath was made for man,
444 ἄνθρωπος anthropos
anth’-ro-pos
from
435 and ops (the countenance, from
3700); man-faced, i.e. a human being; n m; TDNT-1:364,59;
{See TDNT 72}
{See TDNT "the Son of Man" 807}
AV-man 552, not tr 4, misc 3; 559
1) a human being, whether male or female
1a) generically, to include all human individuals
1b) to distinguish man from beings of a different order
1b1) of animals and plants
1b2) of from God and Christ
1b3) of the angels
1c) with the added notion of weakness, by which man is led into a mistake or prompted to sin
1d) with the adjunct notion of contempt or disdainful pity
1e) with reference to two fold nature of man, body and soul
1f) with reference to the two fold nature of man, the corrupt and the truly Christian man, conformed to the nature of God
1g) with reference to sex, a male
2) indefinitely, someone, a man, one
3) in the plural, people
4) joined with other words, merchantman
and not man for the sabbath:
So while it was a sign for Israel, it was far more than that.
God didn't need to rest after creation. So He was setting an example, similar to when Jesus was baptized. And it wasn't a "spiritual" example... He literally took the day off... And Adam and Eve's first experience in life was sharing that day with their Creator.
2. Can someone who does not obey the sabbath according to the law get to heaven?
Why do you say, according to the law? Let me rephrase your question to give it some more poignancy.
Can someone who does not obey God get to heaven?