Megg
From Halopedia, the Halo wiki
Summary
Jaime Griesemer, a designer on Halo: Combat Evolved, gave his girlfriend, Meg Sagi a gift in the form of an easter egg. The egg, affectionally called the Megg, was hidden in Pillar of Autumn Level under a series of bizarre triggers to ensure that no one could find it accidentally. The Megg itself is a heart made from human blood, with an M made from bullet holes in the center.
Images
http://img68.echo.cx/img68/9879/themegg5ym.jpg
