Hi Josie & John,
All I could find out was this:- Charles Riggs & company. The marks of this gunmaking business, trading from 107 Bishopgate, London E.C.,have been reported on 12 bore shotgun cartridges made by Eley Bros, prior to 1914 and sold as The Bishop among other names. The address was often rendered as 'Ye Bishop`s Gate`, which has also been listed as a tradename.
ATB
Bazwong.