Dunwich Horror token
From Arkham Horror Wiki
Dunwich Horror Tokens track the progress of the Dunwich Horror track.
Whenever a monster enters a vortex on the Dunwich board, a token is added to the track and the terror level increased by 1
When the track is full, the Dunwich Horror monster marker is placed on Sentinel Hill.
If the Dunwich Horror is defeated, then the tokens are removed from the board.