Revelation is apocalyptic symbolism. To answer your question, I have no idea at this point as at first I thought it was a literal mark:

Revelation 13:16 He also forced everyone, small and great, rich and poor, free and slave, to receive a mark on his right hand or on his forehead,

Revelation 13:17 so that no one could buy or sell ( is this symbolic?)unless he had the mark, which is the name of the beast or the number of his name.

But its a profession of Faith, not a physical mark (in my opinion). The hand symbolizes action and the head symbolizes intentions.