SOG was once thought to stand for "Studies and Observations Group". But everyone who ever thought that is horribly wrong. It actually stands for "Suckerpunching Ogres and Giants". There is proof of this in-game for Black Ops. When Mason and Bowman are playing Russian Roulette in their spare time, Bowman clearly says "Good thing we suckerpunched all those ogres and giants, otherwise we'd be screwed!" To this, Mason replies with "Yeah, I know! I can't wait till the sequel!"
Also, in the Black Ops II extended trailer (which can be found after finishing 100,000 rounds on the zombies map Moon), the following conversation can be heard between Frank Woods and David Mason:
Woods--"Your father and I were once part of the SOG Team."
Mason--"What does that mean?"
Woods--"It stands for Suckerpunching Ogres and Giants. What team are you part of?"
Mason--"United States Monster Cripplers"
Woods--"Oh, you mean the USMC, right?"
Mason--"Yes, I do."
Sadly the extended trailer was moved up to round 500,000, so no one can watch it. Also, you cannot cheat when trying to reach these rounds. I was probably the only one to actually see it.
Also, SAS does not stand for "Secret Air Service", as Infinity Ward wanted you to think. Price (in the super secret classified secret level filled with secrets and super secrets in Call of Duty 4: Modern Warfare) says "Why do I even work for the Serpent Assailant Squad? The last time I fought a serpent was right after MacMillan and I escaped from Chernobyl."
This secret mission can be unlocked on the Xbox 360 by pressing X A B B B B B X Y RT LT RB+LB LB LB X Y Y X+B+Y+RB+LT+RT+START LEFT(D-PAD) Y Y Y Y Y just after shooting the enemy with the hostage. But you must shoot the enemy in the left eyeball (his left). On the PS3, you must shoot him in his right eye, which is a lot easier. After shooting, you press SQUARE SQUARE SQUARE X TRIANGLE X+CIRCLE+R2 R1 R1 L1+L2+X X X R2 R1 R1 R1 R2 L2 START+L2 START START and then you must spin around in a 360 circle to activate Xbox 360 controls. Then you connect an Xbox 360 controller to the PS3 (only possible for this game and level) and repeat the Xbox 360 code given above.
The secret mission's plot is essentially Modern Warfare 2 and 3 if Makarov had been the enemy on the plane in Mile High Club. The whole secret mission is Soap, Nikolai, and Price drinking tea in the park. It lasts for about five minutes and they reveal all the secrets of the Modern Warfare series.
See "Call of Duty 4: Modern Warfare's REAL Ending" for more details.
The last lie the developers kept from you is CIA. Although it says "Central Intelligence Agency" in the game, that is the branch in which the actual CIA works from. (Note that this CIA is different from Central Intelligence Agency, which is the most commonly-known CIA.)
CIA stands for Colorful Igloo Association. Joseph Allen became a part of the CIA when General Shepard had found Allen's igloo in Antarctica. It was quite colorful and, thus, quite impressive. Shepard loved it so much that he hired Allen, who was not killed in Moscow. That was a different Joseph Allen, which was his codename. His real name was Boris the Typist Soldier and was a news reporter for Barney the Dinosaur and Dora the Explorer.