What the Bible says about Sign Points to Something Unseen

Deuteronomy 6:8

A sign must be something that can be seen, yet it authenticates what cannot necessarily be seen. For example, one may see a sign on the road that reads, "Columbia, South Carolina—77 miles." A person believes the sign, which tells him that Columbia is 77 miles down the road. The sign points to a fact that cannot be seen. Likewise, a person cannot see the law of God written in one's heart, but when such a person obeys God's law, his obedience points to where the laws are, written in the heart, unseen.

John W. Ritenbaugh
The Covenants, Grace, and Law (Part Seven)