Can a Dunedain Mark be passed across the table to another player?

Yes, because the text on the card says "Pay one resource from this hero's pool to move Dunedain Mark to another hero". So, I am pretty sure you can move it to any hero, regardless of who controls the hero, as long as the hero that you are moving it from can pay for it. Somebody correct me if I'm wrong.

You're right. If a card can only be played/passed along cards that a single player controls, that will be pointed out on the card text; otherwise, the card can be passed to any hero, including those controlled by other players.