The mark is both spiritual and literal. Yes in your mind if you betray God and worship another and yes the evil deeds of your hands(works). There is the falling away.
It is also a means of conformity to the merchant system of buying and selling, for without it, you will be told that you can't do either one (which will be a lie). Unless you owe a note of some kind to a bank, then you have participated in usury anyway and better get out from under it now while you can or what you don't own outright will be theirs.
The bible sais the tribulation is for trying the patience and faith of the saints, not for the unbelievers who could care less anyway. They not only gladly accept it, they are part of it. Overcomers who do not take this mark will be granted reign for a thousand years.
Revelation 14
11And the smoke of their torment ascendeth up for ever and ever: and they have no rest day nor night, who worship the beast and his image, and whosoever receiveth the mark of his name. 12Here is the patience of the saints: here are they that keep the commandments of God, and the faith of Jesus.
15Behold, I come as a thief. Blessed is he that watcheth, and keepeth his garments, lest he walk naked, and they see his shame.