PD on a ring commonly represents palladium. Your ring may be palladium-plated if it's PD created around it. HK is usually a trademark that stands for Harriet Kelsall. They style and provide jewellery all around the United kingdom also to other places at the same time.  The Solar refers to https://titusatmdu.thenerdsblog.com/42954521/detailed-notes-on-jp88