The Book of Revelation is multilayered. Certainly, as several posters here have indicated, the “mark” probably had an application to the crisis then existing in the Church, and I would echo others who have indicated that a literalistic interpretation of the mark is most likely absurd. Hence, I wouldn’t think it would have anything to do with a literal mark being forged on our hands, forehead, etc.
On that vein, the most useful meaning to these things is most likely *spiritual *: the Seal of God in Rev. 7 is most likely meant to contrast the mark of the Beast in Rev. 13, both in a figurative sense. Then, those with the seal of God in their foreheads are those who are spiritually faithful to the truths of God, recognizing that, ultimately, the truth emanates from God. Hence, the seal of God is a metaphor for faithful Catholics. Then, the opposite extreme would be the mark of the beast, symbolizing persons who, unlike the faithful Catholics, who are total friends of God, are persons who are total enemies of God, who believe that truth is ultimately determined by man in his sinful nature, and who serve sin, or, associatedly the Devil, as opposed to “the servants of our God”.
There is even perhaps room for certain gray areas inbetween these extremes:i.e., consider the first two “woes” (the fifth and sixth trumpets). In the fifth trumpet, the individuals affected are “tortured” but don’t die, perhaps symbolizing this in a spiritual sense, which would fit with Christian heretics (i.e., mainly Protestants), who, while still possessing the supernatural life of God within them (assuming they are material heretics), are yet “tortured” through their lack of complete truth and lack of five of the seven Sacraments (they are tortured for “five months.”).
In the next trumpet, a third of man is actually “killed,” again, perhaps really spiritually, meaning, they slip into merely “natural religion”, denying the necessity of Revelation or Redemption from God, as in the deism, rationalism, and the “Enlightenment.”
Anyway, it’s just some thoughts. I elaborate a little on my blog, if you care to check out a short article.