I believe this was a series. I read it in the late 90's, but I imagine that it was published earlier than that. It's about a boy who travels to another world/worlds.
I remember him collecting crests of some kind that matched a symbol on his forearm (I think it was on his forearm). Each of the crest-like objects was made out of a different material (wood, glass, metal, etc.). I believe the antagonist was also searching for them.
He may have had a small knife with him for protection...maybe not.
The opening of one of the books has him by the sea heading toward a boat that belonged to a family member. He had a girl with him (not sure of the relation). There was also mention of some menacing polecats in the brush along the way.
That's really all I can remember. Let me know if this rings a bell! Thanks!