Eye Sigil ARG/Legend of Dungeon
Legend of Dungeon is a game developed by wife-and-husband developer Robot Loves Kitty. The game was released on Steam 13 Sep 2013.
The sigil was added in an update 08 Dec 2015.
There is a dwarf in the bottom right corner of the options menu. Clicking it and filling in the password
secret dwarf will make the sigil visible in the options menu.
Puzzle piece is displayed on the 27th floor (secret level of the game) after finding the sigil.
The piece is stored in the game as a texture (map.tex) at a different orientation (and mirroring) than how it's displayed in-game (X and Y coordinates are switched).