PD on a ring ordinarily represents palladium. Your ring could possibly be palladium-plated if it has PD composed above it. HK is actually a trademark that means Harriet Kelsall. They style and design and provide jewellery everywhere in the United kingdom and also to other sites at the same time.  https://collinjasiy.techionblog.com/37142654/jp88-no-further-a-mystery