PD on a hoop normally signifies palladium. Your ring could be palladium-plated if it's got PD written in excess of it. HK is actually a trademark that means Harriet Kelsall. They design and supply jewellery all over the UK also to other spots too.  The Sun refers to the hallmark https://angeloqdqal.uzblog.net/the-ultimate-guide-to-jp88-50650991