In celebration of today’s special date, I have searched the USPTO for patents and trademarks including several 6s, and here is my short list of references for your enjoyment:

Patents:
U.S. Patent No. 6,666,666: “Multi-chamber positive displacement fluid device” - issued December 23, 2003 to Denis Gilbert and Arnoud Struyk. This patent discloses “an improved positive displacement fluid device, such as a pump, having one or more pump sections, the pump sections being adapted for axial stacking which enables high volume, high pressure transport of high temperature production fluid which can contain a substantial degree of contamination.” - LINK

U.S. Patent No. 7,000,666: “Printer” – issued February 21, 2006 to Brent E. Brent et al. This patent discloses “an improved labeler for printing and applying labels which is user-friendly by being low cost, has relatively few parts, is easy to assemble, is easy to load and is easy to use.” - LINK

U.S. Patent D500,666: “Double beam corner support bracket” – issued January 11, 2005 to Richard W. Murphy and John J. Murphy. - LINK

Trademarks:
There are sixteen (16) “live” trademark registrations utilizing “666” – here are a few:

76444053: “666” – registered May 11, 2004 to Atitania, Ltd. (Diana Peterson and Jacqueline Peterson) for “computer software for assigning a universal identification code to communication streams and for assigning a universal identification code to entities that can communicate through one or more communication channels.” - LINK

75538510: “CARS-R-COFFINS 666” – registered September 12, 2000 to Thomas K. Everson for “[m]agazines about bicycles, cycling lifestyles, and how cycling is incorporated into everyday life.” - LINK

76381686: “ROUTE 666” – registered September 28, 2004 to Crossgen Intellectual Property for “[p]rinted materials and publications, namely comic books, comic magazines and printed stories in illustrated form featured in books and magazines.” - LINK