PD on a ring ordinarily represents palladium. Your ring may very well be palladium-plated if it's PD created around it. HK is often a trademark that stands for Harriet Kelsall. They design and provide jewelry everywhere in the British isles also to other sites as well.  The Solar refers to https://elliottnrvad.ampedpages.com/the-definitive-guide-to-jp88-63923864