I have a theory:

Excerpt from the book of Revelations, NIV Bible:

16He also forced everyone, small and great, rich and poor, free and slave, to receive a mark on his right hand or on his forehead, 17so that no one could buy or sell unless he had the mark, which is the name of the beast or the number of his name.

18This calls for wisdom. If anyone has insight, let him calculate the number of the beast, for it is man's number. His number is 666.

6 is man's number. the MoB (Mark of the Beast) is 666.

Look at any barcode you can find, right now, and you'll see 3 sets of lines which are slightly longer than the rest. Most of the time (not all of the time) the first set has the number 6.

Three sets, three 6's. 666.

Oooh, spooky.