In Gears of War 3 for the Xbox 360, there is one secret achievement called Respect for the Dead that you can unlock.
To unlock the Respect for the Dead achievement, in Act 4: Chapter 1 “Ashes to Ashes”, you must make it through the level without shooting, hitting, or otherwise touching any of the Ash Bodies.
If you do this properly, once you reach the stranded camp, the achievement will unlock, and a weapons locker will be unlocked for you.