British Copyright Numbers on Medals

This recent acquisition has an RD number, which I think is a sort of copyright number. I had not seen one before.
The medal is by Arthur Fenwick. The RD number would place the design from late 1905, if I understand the system correctly.
As an aside, I emailed the current president of the G & D Horticultural Society. He claimed that they are about 40 years old and he had no knowledge of any G & D Horticultural Society prior to that time. Strange.
Honors flysis Income beezis Onches nobis Inob keesis
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It looks like something was supposed to be inscribed on the obverse as well.
@291fifth Probably. My guess that it was meant to be a souvenir or a prize that was not received.
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It might have been awarded, but the recipient's name somehow never got on the medal.
Perhaps 'The Guns of August' 1914 interfered.