Final answer:
In the Old Testament, the name of God was to be written on the foreheads of Israel as a symbol of their allegiance to Him.
Step-by-step explanation:
In the Old Testament, it was prophesied that what is to be "written" on the foreheads of Israel is the name of God.
This is mentioned in several passages, including Ezekiel 9:4-6 which states that a mark should be put on the foreheads of the faithful ones.
The purpose of this mark was to differentiate them from the unfaithful and to symbolize their allegiance to God.