Birthmarks

Special people are born with a mark. What these marks mean differ from person to person. But a general vague way to classify these are "classes". Each mark can be put into a class. For example there's Scout, Rogue, Knight, Warrior.

And someones mark is decided at birth. The power of their mark isn't though, that is only known when they use it. The marks aren't as simple as a physical symbol. They give everyone special powers based on the type. But even though people have the same class what appears when using the mark. That's unique to each person.