Cameo Ring with Male Profile

My Grandmother gave me a cameo ring 20 years ago as I always liked looking at it in her Jewellery box. I just wondered a bit more about it as I have read that male figures facing to the left are rarer. It is hard to read the markings on the ring as they are so small but it looks like there is a 375 mark on the top left of the band and the following marks at the bottom - a mark I cant make out, 9, 375, N. There is a slight crack forming in the ring itself so I know that would devalue it. Anyone have any ideas of what the stone is itself? Thanks Zara