Maker of 18k gold ring?

What is the item?
An 18kt quadrefoil ring

Can you please provide all background information?
Ring is very thin. 1.7g
I purchased on Ebay as an antique ring. Want to know if it really is.
What are the markings?
G & upside down G, A crown, 18, a sideways anchor pointing to the left, lower case k

Where are the markings?

In the middle of the shank. On the bottom of your finger when you wear.