Is there such a thing? I'm currently away from books, and a player of mine asks me is there a way that he could gain a proficiency with a martial weapon (he'll be playing a human cleric of Erastil, and he wants to use a Scythe) through a trait.
I am also going from memory, but I do believe there is. It's a social trait. I also believe it might be an Elven trait. So, being a human, you player may need the 'adopted' trait first...
Just trying to help you along. =)
EDIT" Elves pf Golarion campaign guide, is the reference, I think.