Call Sign

Overview

The 'call sign' is a feature that can be traced back as far as  Wing Commander. More recently, it has been seen in  Halo 3 and  Call of Duty: Modern Warfare 2. It is a way of displaying a player's ID, rank and other important mission during gameplay. It also allows the players to have a degree of customization over their online alias in the game.  
 

History

As long ago as 1990, Wing Commander allowed players to assign their player character a call sign to be used in game. As games have become more and more customizable, many games now allow players to not only have a written call sign, but also their own colors, emblems and ranks. Halo 3 was the first major game of the current generation to give players the ability to edit their call sign which was made up of 3 numbers and an emblem.
 
A call sign system can also be witnessed in both  Red Faction: Guerrilla and  Saints Row 2. SR2 has the most primitive call sign system of these, as it only allows you to change a badge. Red Faction: Guerrilla advanced on this idea more, and had backgrounds and foregrounds. Players were allowed to select from different options to make their own sign. However, like Saints Row 2, the sign was only visible before a match - not during it. 
 
The Call of Duty franchise since Modern Warfare 2 has used a robust call sign system. In Modern Warfare 2, players can unlock more 'Emblems' and 'Titles' by completing challenges and objectives online, and these can be used to customize a profile. Black Ops enables people to create their own call sign using template designs and shapes and allows placement for it on their weaponry.