The Call of Duty series has been a bit of a hit for Activision. It started as an entry in the WWII PC first-person shooter sweepstakes of the early 2000's with the original Call of Duty, released in 2003. This was followed by a, well, army of sequels and spin-offs for every gaming device of any note, eventually shaking off its historical warfare roots and moving into modern times. The most recent iteration of the series is Call of Duty: Black Ops II, released in late 2012, netting Activision $1 billion dollars in sales within the first 15 days.
Those who pre-ordered BLOPS2 (as it is affectionately nicknamed) or picked up the special Hardened or Care Package or downloaded the Digital Deluxe editions received a free bonus map called Nuketown 2025. A re-do of a map contained in the previous Black Ops game, it is a 50's style "Model Home of the Future", giving more than just a nod to the ominous, retro-paradise feel of Bethesda's recent Fallout games.
What's pertinent here is that if you run through the map at the start of the level and decapitate all of the lifeless mannequins that litter the landscape within a certain timeframe, a TV suddenly shows the classic Activision logo, and with an Atari VCS/2600 controller appearing in the players' hand rendered in Doom-style graphics, they can play four classic 8-bit games from the company's storied past: Kaboom! (1981), River Raid (1982), H.E.R.O. (1984), and Pitfall II: Lost Caverns (1984).
A nice little nod to their past by Activision, appropriately hidden in a retro-styled map. Don't worry about your team-mates getting upset by you hogging the joystick: you are invincible while you play. Here's a video of the easter egg in action:
Video from FireRockerzStudions
Image from Smith190's Flickr Photostream