Unusual Wiki Cap
This item was awared to a person who reported a serious exploit. At the time, Valve granted a unusual of choice, so the reported opted for the Wiki Cap.
The Wiki Cap is only given to the contributers of the official TF2 Wiki. Since this Wiki Cap was not obtained the way it should, it got a backlash by the Wiki community.
Ultimately, Valve removed this item and person had to choose a different cosmetic, which was a Burning Flames Max's Severed Head.
Source
Unusual Wiki Cap
Team Fortress 2 Level 100 Hat
★ Unusual Effect: Sunbeams
Given to valuable contributors to the official TF2 wiki
https://wiki.teamfortress.com/
( Not Tradable, Marketable or Usable in Crafting )