The Summoner Icon popup says that you can unlock special icons via accomplishing achievements in the game.
As far as I can tell, I've never unlocked a new Summoner Icon, or at least have never received a notification that I have. Is there a known list of the achievements that you need to get in order to unlock new icons, like getting to level 30 (which I'm not yet), getting X amount of Kills/Assists/etc.? What icons can I unlock?