From Team Fortress Wiki
How's that bullet feel? Feel good? Huh? Huh?
— The Sniper testing out his silver bullets
The Silver Bullets is a miscellaneous item for the Sniper. It is two blood-stained stakes strapped to the Sniper's right breast pocket and gives his jacket a larger collar.
This item can only be worn around Halloween or during a Full Moon; at other times of the year, it does not appear in gameplay, unless the server has Halloween mode enabled. However, it can be equipped at any time and can still be viewed on the loadout screen even when it is not visible during games.
October 27, 2011 Patch (Very Scary Halloween Special)
- The Silver Bullets were added to the game.
December 15, 2011 Patch (Australian Christmas 2011)
- "neck" equip region changed to "necklace", added "bullets".
February 9, 2012 Patch
- [Undocumented] Silver Bullets no longer show the Sydney Sleeper bullets
- In folklore, silver bullets are a traditional weakness of werewolves, vampires, and other monsters.
- Vampire hunters traditionally wore high collars to protect against vampire bites to the neck.