The hallmark only tells you who the maker is, nothing else. JewelFreak has answered your question and unfortunately, that's all the information you are going to get short of having a gemmologist actually test the stone.
But even if you can find out further info about the mark, it's not going to tell you with 100% accuracy what the gem is. No one can tell you from looking at pictures on the internet with 100% accuracy what that gem is. You will need to make a choice - whether to spend the money to have it tested by a reputable lab, or not. I think that's what most people are trying to say here. As it is quite unlikely that it is a natural sapphire worth many thousands of dollars, many posters are saying that their advice is not to spend the money to have it tested. However, if you want a definitive answer, that is what you will need to do.
It is also easy to switch out the original stone for something else so as K said, knowing the maker doesn't tell you anything other than who the maker is. I've purchased used settings and put my own stones in.