There are class specific stigmas that allows you to learn skills that you can't train from trainers or give special stats such as increase attack speed/casting speed, more damage etc. You could think of it as talent system of WoW's with more choices and free to customize however you wish to.
Another screenshot here.. it's some stigma stone (this is sorc only stigma stone) I found from a mob. It allows me to learn some spell out of it but not exactly sure what kind of spell it is..
I will find out what it is tonight most likely.. my sorc is pretty close to level 20 :[
