[Rev 13:18 Emphasis added] 18 This calls for wisdom [a person with the Holy Spirit]. Let the person who has insight calculate [a visible mark on the skin] the number of the beast, for it is the number of a man. That number is 666.
One thing we can know for sure according to Revelation 13:18 is that the Mark of the Beast can be analyzed as the Scripture tells us. We can calculate the number that equals or corresponds to the Antichrist’s name. Meaning, everyone will have a visible “Mark” on their right hand or on their forehead which you can look at and see to calculate it.