It has nothing to do with a third eye. It’s recorded numerous times throughout the bible.

Keeping the commandments of God is a sign on the forehead and mark of the believer. In Revelation, the Father sends out angels to mark the forehead of his elect ones. This is also spoken of by the prophet Ezekiel.

The forehead represents ones thoughts or belief and the hand represents ones actions. The name represents authority that we are submitted to, expressed through our thoughts and actions.

Either to the beast or the Creator. Either following the commandments of the Most High through faith in the Messiah or a life of sin and lawlessness.