Hi Diane thanks for your question. They are not British Hallmarks. The Shield with Battlements sounds like a maker's mark, and based on your description, probably US maker.
Gold prices are based on pure gold, 24 karats. Most Jewelry is 14 karat, 18 karat and 10 karat. That's why, gold jewelry, less than 24 karat is worth only a proportion of the 24 karat gold price. A 14k gold necklace, for instance is valued at 58.5% of the 24 karat price of gold.
Aquamarine is relatively soft on the Mohs Scale so you need to make sure you store the ring away from other stones, especially diamonds that may scratch it. I have a friend who has a pale blue aquamarine ring (oval cut) that was passed down from her grandmother, the color of this aquamarine which has not been color treated is a heavenly shade of blue.
