PD on a hoop ordinarily represents palladium. Your ring might be palladium-plated if it's PD penned more than it. HK is actually a trademark that stands for Harriet Kelsall. They design and supply jewelry all around the UK and also to other sites too.  The Sunlight refers to the hallmark https://elliottnrvad.ampedpages.com/the-definitive-guide-to-jp88-63923864