In this discussion I see only hypothesis and a question that remained unanswered
bubba48:
Anyway, while it is/was normal practice for the military, the railways and some industries to engrave the watches issued to their personnel, are there examples of objects other than watches with the acronym C.S.(I) certainly attributable to the Canteen Service? If not, why the watches?
dave:
The watches may be marked as such to facilitate passing through customs whilst travelling; it was not uncommon for service personnel to mark the back of their watches with their personal details for this reason.
bubba48:
This could be correct for the issued watches or for a personal name engraved on the back. But why should Canteen Service do it?
size11s:
I had a nice Omega Seamster 30 marked like that which I bought direct from the chap whose name was on the back. The CS(I) markings though are often only on the inside of the case back and not visible without opening the watch.