That's the letter "P" beneath the queen. It was used in the earlier years to distinguish the use of plated steel planchette.
Yours may well have a red dot on the reverse but it was a solid nickel colour when it was originally released. It appears as if someone was artistically attempting to add a sunrise...PMD (post mint damage).
And

to CCF!
Edited by wildflowerAB
08/03/2016 6:07 pm