Other.
There was a recent discussion about this in the news forum :
http://foru.ms/t5838321-microchips-in-humans-high-tech-helpers-or-big-brother-surveillance.html
This is going to be a visible mark (by Revelation's use of the Greek "charagma"), so it won't just be a chip but could be RFID ink.
However... I now don't believe that will be it. I think it's going to be a lot worse than just a RFID chip. I never really understood, until I heard some things recently, this verse :
How can death elude someone? Surely someone can just go up a cliff, or on a roof and jump, right?! Not if you are controlled through your mind, or you are physically unable to control all your actions through technology.
Forgetting about the mind control possibility for now, technology is there to control actions right now... Look at the
plans to create moth spies with technology built in from the pupa stage - where moths can be controlled by remote joystick, fly into enemy territory and send back audio! This has already been done on other animals, so the technology
is there.
So, RFID - probably not, at least not on it's own. Whatever you think it will be, I don't think we've seen anything yet!