PD on a ring commonly represents palladium. Your ring can be palladium-plated if it has PD composed over it. HK is often a trademark that stands for Harriet Kelsall. They layout and provide jewelry all around the British isles and also to other locations as well.  Can “JP” also stand https://elliottrcmyg.pointblog.net/a-review-of-jp88-83662164