The Royal Naval Reserve Decoration

The Decoration for Officers of the Royal Naval Reserve known as the Reserve Decoration (RD) was a medal awarded in the Royal Naval Reserve of the United Kingdom to officers with at least fifteen years of active duty. The medal was instituted in 1908.
The medal had an oval medallion, consisting of the cypher of the reigning monarch in silver gilt surrounded by a silver rope tied with a reef knot at the base and surmounted by a gilt crown which acts as the ribbon suspension, hung from a ribbon which was dark green until 1941 and green edged white thereafter. Originally, fifteen years' service was required (not counting service as a midshipman), with wartime service counting double. Clasps to the Reserve Decoration were awarded to recognise further periods of 10 years service after the first award. When just the ribbon of the Decoration was worn, each clasp was indicated by a silver 'rosette' on the ribbon.
The RD and the Royal Naval Reserve Long Service and Good Conduct Medal for RNR ratings were both replaced by a combined-services Volunteer Reserves Service Medal on 1 April 1999.
https://en.wikipedia.org/wiki/Decoration_for_Officers_of_the_Royal_Naval_Reserve