thanks so much for writing in! The letter "A" in a circle could honestly mean lots of things, it could be a sponsor mark, which is the registered mark the company that submitted the article for hallmarking uses, or maybe it's a Date Letter, which depicts the year the item was hallmarked. More information about the type of jewelry, the material it's made from, etc. etc. the more info you can find out the better chances of working out a hallmark determination. A photo of the mark if possible, will also help.
In the meantime, please have a look around the site.
