...we have letters for ratings, too?
The "official" rating AFAIK is the age you need to be to watch the movie (14, 18, or any). I haven't heard of any restrictions on Passion, though this doesn't mean that there aren't. The 14 is handed in a semi-random fashion among movies that feature some degree of violence or sex. The 18 is automatically used for pornography, but not much else. Overall, it's an unreliable system that everyone ignores.
Then there is the system used for rentals, which again uses age but is more flexible and just a guideline, not a law. And again, thoroughly ignored.
Then there is a system used for broadcasts on major networks, which uses colors (green/yellow/red) and is somewhat more reliable and again only a self-regulation thing. Red means something that would probably get a 14 at the cinema (stuff that would get an 18 doesn't get onto major networks, of course).
But I have no clue as to what "G" means.