Maybe it can be something along the lines of:
Dominion Icon - Acquired from winning over 100 games on Dominion before it retired, you madman.
Eternal Journey Icon - Acquired from the store for 250 RP. Much better than a Shen skin, amirite?
Kiko Icon - Acquired from the First Star Ahri Bundle. And another one!
Beta Tester Icon - Acquired from participating in League of Legends' beta test and being one of our top testers.* Thanks for not leaving us after 5.16!
And so on, and so on... It should be pretty easy to add, and it won't cost much resources besides actually finding where each icon comes from, which is probably easy for Riot to do - they made them in the first place.
*Fixed, thanks /u/Black-_-Wing
