Isa 49:15-18 "Can a woman forget her nursing child, And not have compassion on the son of her womb? Surely they may forget, Yet I will not forget you. See, I have inscribed you on the palms of My hands; Your walls are continually before Me."
"I have inscribed you on the palms of My hands"
In the verse, "Behold, I have inscribed you on the palms of My hands" (Isa 49:16), there is an allusion to the ancient custom of puncturing ornamental figures and mementoes upon the hand, arm, and forehead, and coloring the punctures with indigo, cypress, etc. This gives us the figure of Zion being as close to God as He is to Himself, and facing Him amid all the emotions of His divine life. - Unger's Bible Dictionary
In this figurative way of God expressing His love for His people, the Lord is in essence saying that He will never forget Zion, the city (people) of God. They are inscribed (engraved) upon the palms of His hands so that they will always be in His sight and kept as an everlasting remembrance.
It is most probable that this expression is referring to an actual custom among the Jews who actually tattooed their hands or arms with paintings of Jerusalem or the Temple, thus they would always have a remembrance ever before them. This view is accepted by most scholars and these palm painting representations were called "ensigns of Jerusalem" and were performed in this sort of manner:
1. They would have an impression on a block of wood of something relation to the city such as the Temple, and and they print it onto the palm or arm with powder or charcoal.
2. Then they would take two needles tied close together, and dipping many times in certain inks they would make small punctures quickly and accurately all along the lines of the figure they have printed, being careful not to draw blood.
3. Then they would wash it in wine once the figure was finished.
note: Strongs Hebrew dictionary renders the word "palms" as (Heb. kaph OT:3709 from OT:3721) the hollow hand or palm as distinguished from its fingers, thumbs, and back, and the word "inscribed" as (OT:2710 chaqaq ) a primitive root meaning to hack or engrave.
This verse teaches us that God constantly cares for and remembers His people, using an imagery that was familiar to the ancient custom of the day. Even in the midst of the most terrible trials, as in the background of this verse, He will always remember His beloved. Just as their city walls were built for safety, so our safety and protection depends upon His continual care.
The wounds in Christ's hands (palms) when he was crucified is a clear message hinting (remez) back to this ancient custom and bringing forth the message that the Lord will always cherish and protect those for whom he suffered and died, and His remembrance of us is as close to God as He is to Himself.
Bibliography on Ancient Customs
The Art of Ancient Egypt, Revised by Robins, 272 Pages, Pub. 2008