Yes. a hallmark is an assay mark - the M in a shell is a maker's mark.
There are several elements to a UK hallmark - the maker's mark (mine is WMG in a classic cartouche) which is unique to that one person, then there is a year mark (a letter in a specific typeface and possibly also a shape) a place of assay - lion, leopard etc etc and a specific mark for what the metal is and what proof. sometimes there are extra marks such as the Queen's head on silver for her silver jubilee and gold for her golden.
A sponsor/maker's mark is a more powerful and unique mark than any trade mark in fact as mine is mine for all time (cor!) and the roll of the registering hall is final on the matter, while a trademark can be changed, lost, argued about in court, passed off etc etc
nb, if I send something for marking and it does not come up to proof it will be damaged so as to be unsaleable as a piece (only fit for scrap). Any piece sent for checking to a hall which carries a faked hallmark and which does not come up to proof will be similarly marked/damaged. That includes using too much low melting point (easy and extra easy) solder.