A general tip regarding armor before I work on the map landmarks:
When you see a downed enemy who still happens to be wearing armor, try not to go for the special execution or haphazardly shoot the legs to execute from a distance. You don't want the player getting away with his armor intact, as you get to keep armor when you respawn.
Shoot the upper body until the armor breaks, and only then should you execute. You can also try breaking the helmet with a headshot while the player is downed, but it's hard to do when in the middle of a firefight or if the player is crawling away. There are those who get downed and just give up by kneeling in place. Take the opportunity to blast their helmets off.
If a teammate performs a special execution before you shoot the armor off, don't worry. Before the animation finishes with the enemy being executed, you have a couple of seconds to break the armor.