Skulls Taken!
From Halopedia, the Halo wiki
Skulls Taken!
Skulls Taken! is an achievement in Halo: Combat Evolved Anniversary. It is awarded for claiming half of all campaign skulls.[1] It is represented by two human skulls on top of a white five-pointed star.
The Achievement is worth 25 Gamerscore.
Trivia
The name of the achievement is a direct quote from the announcer in Halo: Reach's Headhunter gametype when players pick up a skull.
Sources