The Book of Revelation tells us that the End of Days will include the appearance of a False Prophet who will lead the apostate churches, and his friend the Beast (a political leader who will rule the ten nations that grew out of the Roman empire, as predicted in the image of the ten toes in Nebuchadnezzar's vision). According to Revelation 13:17-18:
Since a 'score' is 20, 'Six hundred threescore and six' is 666 = the Number of the Beast.
Fundamentalists spend a lot of time thinking about that number. Below is a picture of the police branding the mark of the beast, the number 666, on a poor victim. Fundamentalists also find the number 666 in the most unlikely places, 'signs of the times'. For example, they have located a 666 pattern in barcodes....and even in the old symbol of the United States Postal Service.
CLICK TO ENLARGE