I’ve been squinting for some time now looking at the mark and going through the reference works I have (and could find online).
This is the hallmark of a hot water jug, as far as I can tell silver (checked for the usual wear / tear and so on).
It seems that there are two sets of hallmarks on top of each other, as well as four recognisable characters ‘MONS’, which could be the Belgian town of Mons, but seems more like an abbreviation of ‘Montrose’ (as there seems to be a rose as the third mark).
Hope someone is able to help / speculate?
(photo hosted at Flickr):
Thanks from a newbie / amateur