A plain steel or silver ring on either ring finger (in any country) can also mean you're saving yourself for marriage. This is called a "promise ring" or "purity ring".
EDIT: Well, when I say "in any country", I only know for sure that it's a known concept in Australia, New Zealand, and America. But that probably covers most nationalities of the people here on the Escapist forums.
Another EDIT: By "saving yourself for marriage" I mean that you're making a commitment to save your virginity for after you are married - it doesn't necessarily mean that person has a particular person in mind - just that they're interested in long-term relationships.