Wolfy
There were three types of people: Kissers, Namers, and Tattooers. You either had a Tattoo that matched another's or a Name marked above your heart. If you didn't, then you were a Kisser, recognizing your soulmate at first touch or kiss, as innocent as the person wanted it to be.
As soon as you were born, it was obvious which category you fell into.
Sirius had a Tattoo.
Remus didn't.