I remember something similar from a course I took in college, perhaps, or something I read later. Whatever it was it went even further with the symbolism: the idea was that the mark on the forehead represents the way in which one thinks, and the mark on the hand represents the way in which one acts. The takeaway was that it wasn't so much that one would be forced to make a claim of some sort in order to participate in the system of commerce, but rather that by participating in the system one is already marked by it.

I liked this interpretation because it changed the emphasis from one of watching out for some piece of technology or some bitter-tasting oath that you'd have to profess--both of which seem like they'd raise red flags to even the most casual Christian and are therefore unlikely to be much of a real threat--to one of looking inward and evaluating how your own participation in any system of exchange is subtly affecting the way you look at the world and at other people. (You can also see how this isn't terribly compatible with the brand of prosperity theology that has infected some branches of American Protestantism.)