Oh, don't get paranoid. Reread the Revelation to St. John. The mark of the beast damns the recipient--meaning repentence is impossible. An RFID tag the receipt of which can be repented of with a flick of a knife-blade (albeit at some self-inflicted pain, but that always goes with serious repentence) isn't it.
I'm betting on something with a neural-computer interface. The recipient won't be able to repent because the recipient's will will be submerged by whatever he or she is linked to by 'the mark'.
Don't be so certain. In Rome, life was a lot easier for Christians who would recognize the (quasi) diety of the emperor. This may mean people who decide to 'go along to get along', and reap the benefits, are accepting the 'mark'.