Naturally, you may choose to remain in your ignorance. But at least consider where the Bible mentions the purpose of marks on foreheads. It occurs in Judaism, as early as Exodus.
Exodus 13
It shall be as a sign on your hand and a a reminder on your forehead.
Exodus 13:16 –
Let this, then, be as a sign on your hand and as a pendant on your forehead: With a strong hand the Lord brought us out of Egypt (i.e. slavery)
Deuteronomy 11:18:
Therefore, take these words of mine into your heart and soul. Bid them at your wrist as a sign, and let them be a pendant on your forehead.
All these were a sign that these people worshiped God.
Now, let take a look at Revelation 13:16 (New Testament)
where Nero decreed a sign that he was the god to be worship be on the people’s foreheads:
"He (Nero) causes all, both small and great, rich and poor, free and slave, to receive a mark on their right hand or on their foreheads".
In the Roman Empire during Nero’s time, no one could buy or sell unless they had Nero’s mark (the sign of the beast that he was to all Christians) on their foreheads.
In the Old Testament, ashes were a sign of penance. The cross is a sign of God’s redemption of mankind, therefore a sign of God. I understand that Jews hold no belief that God, Himself became man to share in our humanity, and continually showed his love for his people even through death. Again, Jews hold no such belief, but it is the heart of Christianity and Christian teaching.
Jews can sincerely and respectfully say, "We hold no such belief" while respecting the faith of Christians. The reasoning and logic Christians have for belief Jesus was the begotten Son of God, a part of Him from the beginning of time, is immense, and this, too, deserves respect.