Hello, I agree with Orthogonal, your photo shows makers marks that are likely to be those of “John George Graves” the Sheffield industrialist. The mark you have posted, is as illustrated on 927-1000’s silver plate reference section and also shown on the “silvercollection.it” web site.
The “CS” as you intimate could be “copper silver” but a mark resembling a bona fide silver makers’ mark could have economic advantages for selling electroplated products. Also incorporated in the big “arches” mark is a “crab-like” pseudo silver mark, possibly there for the same reason.
I have recently come across a spoon with this very similar mark.
The detail is not as well preserved as in your photo and the crab appears replaced with a "dot". There is also 1 less “arch”. The obvious assumption is that this is another mark of “J G Graves”. However as “Dognose” has suggested and shown in various other posts that illiteracy and maybe commercial pressure in the early electroplating period often gave rise to “copying” though at the start of the 20th century this should be less likely.
Yours
Fishless
Ps. There is another post about “J G Graves” on the forum but in “Silverplate Trademarks Worldwide" giving a further perspective on “J G G” marks.
