Cold-Blooded is a Tier 2 perk that appears in Call of Duty: Modern Warfare 2. When used, enemy vehicles will not detect the player. It's commonly used in Anti-Aircraft classes along with Stinger missles.
The Pro version of Cold-Blooded takes away the enemies to see the red name above the player as well as the red of the cross-hairs when pointed at the player. If the player lies prone, it'll appear as if he's a corpse.