It's a shamrock.

Apparantly the image was taken from the Harry Potter and the Goblet of Fire book. I'm guessing the US or some other foreign edition or something, because the UK one didn't have any illustrations.

The illustration itself refers to the supporter hats for Irish fans in the Quidditch World Cup (Ireland vs. Bulgaria).

:P

Plus it was fitting with St. Patrick's day.

How do you like this WoW Undead icon? :D