There are 30 of these emblems scattered throughout the game, but they are well hidden and require a keen eye to discover them all.
To "acquire" the emblem you must destroy it in some way, either by shooting it, knifing it or using a grenade. Once shattered, you must complete the current chapter in order for it to be added to your current tally. It's worth noting that even after you have destroyed one, if you replay the chapter it will appear again, but this does not mean you have to destroy it again in order to keep it. Most unlockable content requires a certain number of these emblems to be destroyed.