According to McConkie and Parry, perhaps due to the high visibility of the forehead, many persons in antiquity have placed identifying marks upon their foreheads. This was done both to distinguish themselves from others and to identify a peculiar social stance or position. Such was the case of prostitutes of the late Old Testament period who distinguished themselves with a mark on their foreheads (Jeremiah 3:3; Ezekiel 16:12). In the Book of Mormon “the Amlicites were distinguished from the Nephties, for they had marked themselves with red in their foreheads after the manner of the Lamanites” (Alma 3:4,13,18). Aaron the high priest, wore “a plate of pure gold” on his forehead. This emblem had written upon it the words “Holiness To The Lord” (Exodus 28:36-38).
Both righteous and unrighteous causes have employed marks in the forehead to identify their followers. At times of righteousness the Saints of God will reign in the celestial kingdom, with the name of their God written upon their foreheads (Revelation 22:4). [Joseph Fielding McConkie & Donald W. Parry, A Guide to Scriptural Symbols, pp. 53-54]
Alma 3:13 They also had a mark set upon them … even a mark of red upon their foreheads ([Illustration] Marking the Forehead with the Signs of Pagan Gods. [The Church of Jesus Christ of Latter-day Saints, The Life and Teachings of Jesus & his Apostles, Course Manual for Religion 211-212, p. 465]