The mark has already been identified. It's called the UPC. Study the lines and notice that on the long form UPC three sets of lines are always identical and always not represented by the numbers shown at the bottom of the code. Those three sets of unrepresented lines each represent the number six, thus three sixes.
Here's an illustration:
LINKY
notice the lines highlighted in green. They are known as "guard bars" and like I said, are on EVERY long form UPC.
Now look at the short form
HERE
The guard bars are only on the ends on this one , but the numbers represented between them are a set of six, thus making another 666.
KJV
13:16
And he causeth all, both small and great, rich and poor, free and bond, to receive a mark in their right hand, or in their foreheads:
Notice IN not on as has been translated into newer "versions" of the bible.
13:17
And that no man might buy or sell, save he that had the mark, or the name of the beast, or the number of his name.
Every product in this country has a UPC associated with it. When we purchase it, it is metaphorically "in" our hands and minds. Therefore "in" our hand or forehead.
The number of the beast has been right in front of us for years. The first UPC marked item ever scanned at a retail checkout (Marsh's supermarket in Troy, Ohio) was at 8:01 a.m. on June 26, 1974. And you don't need the mark on your person in order to have it's influence "upon" you.