Welcome to the GMB.
The initial 'JG' is probably the maker's name of the silver, but probably not the glass. The figure '18' might relate to the quality of silver.
A few ways you can help further: provide a photograph and indicate whereabouts you are based. If there's no hallmark on the silver, it is probably not British. If there is a hallmark, please provide details as this may help age the piece.
See the initial messages at the top of the forums for instructions on how to post photos.