There is no mark for people today or in the future. That's what I meant by there is no mark. The mark has already took place.
I believe the mark concerns the institution of Emperor worship as demanded by the Caesars of the Roman Empire. Through time, the Caesars demanded that all men bow the knee to them, and provided certificates of proof that one had paid due homage. Those attempting to travel or conduct business without said certificates were subject to imprisonment, persecution, or death.
One must always bear in mind that the Scriptures were always pertinent to the people to whom they were written. The early church would have been familiar with the ideas conveyed in the passages.