From Team Fortress Wiki
Bill's Hat is a promotional headwear item for all classes. It is a slightly worn team-colored beret, with the yellow shield insignia (or "flash"), of the U.S. Army's 1st Special Forces Group. It is styled after the hat worn by the eponymous William "Bill" Overbeck in Left 4 Dead.
- Bill's Hat was added to the game
- This hat was made paintable.
- [Undocumented] Added a community-contributed description for this hat.
- The hat's painting texture was improved.
- Made this hat always tradable.
- Fixed not being able to see the correct colors for painted hats when running with DX8.
- [Undocumented] This hat can now be used as a crafting ingredient.
- Bill's Hat was awarded to players who had pre-purchased the Valve title Left 4 Dead 2 on Steam or for PC through GameStop before November 17, 2009.
- The hat description was written by Calvary for the Hat Describing Contest.
- Bill's Hat has its own intricate backstory: "While conducting a science experiment on parallel dimensions, Bill's Hat fell off a table into the Team Fortress universe."
- The beret flash on the hat is that of the 1st Special Forces Group which is based out of Joint Base Lewis-McChord near Valve's headquarters in Bellevue, Washington.