Call of Duty 4 only had clan tags, but Modern Warfare 2 takes it further by allowing you to customize your own "callsign". The emblems and titles are unlocked by just playing the game; the Xbox 360, PlayStation 3 and PC versions unlock everything the same way. For example, you gain the suppressor title by killing people with silenced weapons.
As you unlock more emblems and titles, you can mix them up anyway you please.
