Dear Linda
If its not bogus it could be the Britannia mark for silver 958,
applied from 1696 to 1720. When all silver holloware was required to
be of a higher standard than coinage which was 925 (Sterling) This
was done to stop unscrupulous artisans melting the coinage down.
Usually there is a stamp with the image of Britannia on it. Can’t
think of anything else.
Regards
Hamish