Properly understanding the Apocalypse of St John is a difficult thing - especially in this current age of rampant fantasy based upon the end of the world (not the least the fantasies put forth as Bibical exegesis by those who are alien to the Church). In order to approach and understanding one must forget all the nonsense that is out there and begin anew drawing only upon the fathers and the tradition of the Church.
Here is an excerpt from a brief article on the Apocalypse by the late Bishop Alexander (Mileant) of South America that touches on the question of the mark of the beast:
The seal of the beast (Rev. 13:16-17, 14:9-11, 15:2, 16:2, 19:20, 20:4). In the language of Holy Scripture, to bear upon oneself a seal (or a mark) denotes belonging to or being subordinate to someone. We have already mentioned that the mark (or the name of God) on the forehead of the faithful denotes their being chosen by God and consequently having God's protection over them (Rev. 3:12; 7:2-3; 9:4; 14:1; 22:4). The activity of the false prophet, which was described in the thirteenth chapter of the Apocalypse, convinces us that the kingdom of the beast will be of a religious-political nature. In creating the union of various governments, it will simultaneously propagate a new religion instead of the Christian faith. Therefore, the submission of oneself to the antichrist (allegorically speaking, by taking upon one's forehead or right hand the mark of the beast) will be tantamount to renunciation of Christ, which will result in the forfeiture of the Kingdom of Heaven. (The symbol of the mark is drawn from ancient customs, according to which warriors burned upon their arms or their foreheads the name of their commander, and slaves, either voluntarily or by force, were branded with the seal of their master's name. Pagans devoted to some deity often bore upon themselves the tattoos of that particular divinity.)
It is quite possible that during the time of the antichrist a perfected computerized registration system will be introduced which would be similar to modern bank credit cards. This state-of-the-art registration will have an invisible computerized code imprinted not on a plastic card as it is now, but directly on the body of the individuals. This code, read by an electronic or a magnetic "eye," will be transmitted to a central computer that will contain all pertinent personal and financial information regarding that person. Thus, the imprinting of personal codes directly on individuals will replace the need for money, passports, visas, tickets, checks, credit cards and other personal documents. Thanks to individual encoding, all monetary operations such as payment of salaries and payment of debts can be performed directly in the computer. In the absence of money, robbers will have nothing to take. It will be pre-eminently easier for the government to control crime because people's movements will be known thanks to the central computer. It appears that the positive aspects of this system of personal encoding will be used to introduce the system. In practice, however, it will also be used for religious-political control over people "when no one shall be able to buy or sell, except those who have such an imprint" (Rev. 13:17).
Of course the idea of stamping codes on people is speculation. The essence is not in electromagnetic markings but in fidelity to Christ or our betrayal of him! Throughout the history of Christianity, pressure on believers from antichristian authorities has taken on the most varied of forms: the bringing of a formal sacrifice to an idol, the acceptance of Islam, the joining of a godless or an anti-Christian organization. In the language of the Apocalypse, this acceptance of "the seal of the beast," is the acquiring of temporary advantages at the price of the renunciation of Christ.
Notice that the key element in receiving the mark of the beast is a conscious and intentional renunciation of Christ. You can't get tricked into doing this without your knowledge - you have to directly and purposefully renounce Christ to obtain the mark of the beast. So unless there was a "check off" on the application for that credit card for renouncing Christ, you do not have the mark of the beast.
Another thing that the Fathers tell us about this mark is that the hand and the forehead denote our thoughts and actions and so the mark isn't about what is put on the outside, but rather what comes out from the soul. Remember, "Not that which goes into the mouth defiles a man; but what comes out of the mouth, this defiles a man" (Mt15:11) That is to say that we are not defiled by things which are put on from the outside (for example a physical mark placed upon us by someone else) but rather we are defiled by that which comes from the inside - our own thoughts and actions.
Another good book on the Apocalypse is by Archbishop Averky of Jordanville, translated by Fr Seraphim Rose (available I believe through St Herman Press). There is now coming out from Zoe Press a series of sermons on the Apocalypse by Archimandrite Athanasios Mitilinaios. There are three volumes in print and at least one more (maybe two) still to come. Forget your protestant and Hollywood fantasies and embrace the tradition of the Church.
Fr David Moser