Modern Warfare II is packed with hidden details, references, and fun easter eggs for players to discover. These range from subtle nods to previous Call of Duty titles and pop culture to more elaborate interactive sequences. Exploring maps thoroughly and paying attention to environmental details can reveal these secrets, adding an extra layer of enjoyment to your gameplay experience.

- Campaign References: Keep an eye out for mentions or visual cues related to characters and events from the original Modern Warfare trilogy.
- DMZ Hidden Areas: The Al Mazrah map in DMZ contains several hidden bunkers, caches, and unique locations that often require specific keys or puzzle-solving to access, yielding rare loot.
- Weapon Charm Easter Eggs: Some weapon charms have interactive elements or hidden messages when inspected closely in the Gunsmith.
- Arcade Cabinets: In certain multiplayer maps or safe houses, you might find playable arcade cabinets with mini-games or classic Call of Duty titles.
- Loot Crate Secrets: Occasionally, specific loot crates in DMZ or Spec Ops might contain unusual items or trigger unique audio cues.