What’s a good symbol set for buttons to expand and contract parts of a hierarchy?

The Mac Finder, in hierarchy view, uses a triangle, or arrow, facing right to indicate not-expanded, down to indicate expanded folder. It could be considered counterintuitive because it points to the current state as opposed to what it will do. This is for a website navigation, so would non-Mac users understand this?

Would simple "+" to expand, changing to "-" when expanded, be more universally understood?

Any other good symbol sets for these kinds of actions?