Seans black leather jacket is a relic from his past. May be he could be reminded in some way of his past by the belt too, even if it is new. Perhaps the belt resembles one he lost and with it he lost his "wild" manners. So the belt would be a sort of a symbol for something he lost in his life (and can be regained by Viggo?)
OK- the idea came because of a novel I read this afternoon- BUT: I never wrote a good story myself. So don`t think about it too seriously. Bye- good ideas!