From Team Fortress Wiki
The Griffin's Gog is a miscellaneous item for the Spy. They are a pair of large brown goggles with reflective lenses.
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 Griffin's Gog was added to the game.
- The Griffin's Gog are based on goggles worn by Griffin, the main character from the novel The Invisible Man, upon which the Invisible Rogue costume set is based.