Have a saved game file from Rainbow Six: Vegas or Splinter Cell: Double Agent on your hard drive or memory card to unlock extra headgear items unique to each of those games available when you customize an online character.

ICS-PL Helmet: Rainbow Six: Vegas saved game file.
J-E FO Helmet: Splinter Cell: Double Agent saved game file.
PAS GT Helmet: Rainbow Six: Vegas saved game file.
Tactical Shemagh: Splinter Cell: Double Agent saved game file.

Successfully complete the game to unlock all weapons in Quick Mission mode.

Successfully complete a level to unlock its theater options.

Unlock 5 Decorations.

Unlock 10 Decorations.

Successfully complete the indicated misison to unlock the corresponding music video:

Gimme Danger: Mission 1
Battle Axe: Mission 3
Hero: Mission 7

Successfully complete the indicated task to unlock the corresponding Decoration:

Act 1 (elevated risk): Successfully complete Act 1 under elevated risk.

Act 1 (low risk): Successfully complete Act 1 under low risk, normal risk, or elevated risk.

Act 1 (normal risk): Successfully complete Act 1 under normal risk or elevated risk.

Act 2 (elevated risk): Successfully complete Act 2 under elevated risk.

Act 2 (low risk): Successfully complete Act 2 under low risk, normal risk, or elevated risk.

Act 2 (normal risk): Successfully complete Act 2 under normal risk or elevated risk.

Act 3 (elevated risk): Successfully complete Act 3 under elevated risk.

Act 3 (low risk): Successfully complete Act 3 under low risk, normal risk, or elevated risk.

Act 3 (normal risk): Successfully complete Act 3 under normal risk or elevated risk.

Master Tutorial Challenge 1: Kill all enemies without getting hit.

Master Tutorial Challenge 2: Kill enemies with one headshot per enemy.

Master Tutorial Challenge 3: Kill the tank using only one satchel charge.

Master Tutorial Challenge 4: Have your team kill all five enemies.

Mission Accomplished: Successfully complete all secondary objectives.

Single Player Master: Unlock all other single player Decorations.

Tutorial Walkthrough: Successfully complete the tutorial.

Successfully complete the indicated task to unlock the corresponding decoration:

Bullz Eye: Have 100% accuracy.

Hawks Eye: Acquire all intels out of combat.

Iron Man: Do not get hit during the mission.

Predator: Have all fights engaged by you.

Team ELITE decoration: Have no teammates hit and have 50% of the enemies dead by your team.