Edinburgh Silver

Hi,
I’ve just acquired two Georgian Silver Celtic Point Dessert Spoons.
They are hallmarked for Edinburgh - Town mark, Standard (Thistle mark) date letter W for 1802, Duty mark and maker “I.M” that I cannot identify
In addition the spoons are also stamped with an “M” - no punch mark just a struck letter.
Any ideas on the maker and the additional M mark?
Any help appreciated