

weight 14.7g diameter 34.9mm, debased silver
What is the significance of the "M" stamped under the king's head?
For your interest, here is a contemporary forgery of the same coin:


weight 14.1g, diameter averages 35.2mm
There are still faint traces of the silver wash on it. I belive the holed was bored through to show the base metal under the wash, so it could not be used.