Exodus 13:16
15 When Pharaoh stubbornly refused to release us, the Lord killed all the firstborn in the land of Egypt, from the firstborn of people to the firstborn of animals. That is why I am sacrificing to the Lord the first male offspring of every womb, but all my firstborn sons I redeem.’ 16 It will be for a sign on your hand and for frontlets on your forehead, for with a mighty hand the Lord brought us out of Egypt.” 17 When Pharaoh released the people, God did not lead them by the way to the land of the Philistines, although that was nearby, for God said, “Lest the people change their minds and return to Egypt when they experience war.”
Isaiah 44:5
4 They will sprout up like a tree in the grass, like poplars beside channels of water. 5 One will say, ‘I belong to the Lord,’ and another will use the name ‘Jacob.’ One will write on his hand, ‘The Lord’s,’ and use the name ‘Israel.’” 6 This is what the Lord, Israel’s King, says, their Protector, the Lord of Heaven’s Armies: “I am the first and I am the last, there is no God but me.
Notes and References
"... What is the nature of the mark on the hand? Which hand is meant? According to Jewish tradition the left hand. The interpretation rests on the unusual form in 13:16, understood as ‘the hand that is weak’ (‘to be weak’) = the left hand. The right hand, being the most important hand, would seem more likely (compare Revelation 13:16). Considering the nature of the mark on the head, is it not more likely that it is strictly an ornament? The mark would seem to be the sign of membership in the cult of a god (Isaiah 44:5; Revelation 13:16; 14:9). Also, here one could think of a tattoo or brand or a painted mark (compare Isaiah 44:5; 49:16) ..."
Houtman, C. Historical Commentary on the Old Testament: Exodus (p. 219) Kok Publishing, 1993