Question for the mods.

[Rocket Propelled Rocket]

I've noticed those little "nick names" under out user names. For most people it's just "gamer" but for others it's something different. I know that there isn't a way to change them, but how do people get them? Do the mods change it on their own? Do they have to earn it? Does it change depending on how many posts you have?(Doubt that one)