Necklace From My Father

Hello. This necklace was a late 1970's gift to me from my father, who passed away over 30 years ago, so I know nothing about it. The colors may be enamel. The main round piece measures 2" (this size excludes the 20 small individual round pieces). The reverse has a raised hallmark (HMS inside a square with four cone shapes at the top). If anyone has any information on this item, I would truly appreciate if they might find the time to share it with me. Kind regards, Lyn.