PD on a ring ordinarily signifies palladium. Your ring could be palladium-plated if it's got PD written more than it. HK can be a trademark that means Harriet Kelsall. They structure and provide jewellery everywhere in the UK and to other areas likewise.  State hallmarks: Some countries have their unique hallmarking https://garrettalxis.ampblogs.com/the-ultimate-guide-to-jp88-73728955