This marking is spoken of in two separate locations in scripture. In one location it is spoken of as a sign of following YHWH’s law:
And it shall be for a sign unto thee upon thine hand, and for a memorial between thine eyes, that YHWH’s law may be in thy mouth: for with a strong hand hath YHWH brought thee out of Egypt.
The other location it is spoken of as a mark which one receives which shows you are following the Beast.
16 He causes all, both small and great, rich and poor, free and slave, to receive a mark on their right hand or on their foreheads, 17 and that no one may buy or sell except one who has the mark or the name of the beast, or the number of his name.
There is a single distinguishing feature which differs between those who follow His law and those who do not. The Sabbath day.