Customization has featured in previous Call of Duty's, but not to the extent of Call of Duty: Black Ops and the lesser extent of Call of Duty: Modern Warfare 3, with Clan Tags in Call of Duty 4: Modern Warfare, Call of Duty: World at War, Call of Duty: Modern Warfare 2. Another feature of Customization in Call of Duty: Modern Warfare 2 was Callsigns which is also present in Call of Duty: Black Ops.
Customization is featured heavily in Call of Duty: Black Ops, it allows the player to customize their weapon, their Red Dot Sight's color, size and the dot itself, their appearance (although only mildly) via their tier one perk and face paint choices. They also have access to a highly customizable Playercard and can create their own totally unique emblem using in game clip art. The player can filp, rotate, reflect, scale, and change the color to their liking. The player has twelve "layers" that can contain 1 clip art each. The layers must be unlocked by level, and bought with COD points. They do not reset if the player decides to prestige, but any layers not purchased will still be locked upon entering the next prestige.
Customization is downplayed, but still possible, Call of Duty: Modern Warfare 3. The game allows players to select A Weapon Proficiency, Attachment (or two if using the Attachments proficiency), a Red Dot Sight reticle (If using a Red Dot Sight), and a camouflage for their gun.
In Call of Duty: Black Ops II, customization is once again a key component of Multiplayer. Players can create emblems in a similar manner to Black Ops, but now 32 layers are available with more features. After prestiging any gun once, Clan Tag becomes available to be engraved on the gun. Similarly, prestiging a gun for a second time unlocks the ability for emblems to be placed on it. The usual customization also returns, including backgrounds, sight upgrades, and gold clan tags for high-ranking ELITE clans.
In Call of Duty: Ghosts, customization is featured to much more of an extent then in previous games of the Call of Duty series. Players can create custom characters and emblems (although emblems are only available to clans). Create-A-Soldier is similar to Create-a-Class, but offers the feature to customize the character as well as the weapon. Character customization is done by adding different vests, masks, clothes and changing the gender, the feature offering over 20000 different combinations. Emblems return as normal from previous iterations in the Call of Duty series, but custom emblems are only available in clans.