That would be the
Filets or Thread pattern. Fiddle Thread or
Filets Violon would have a waisted (pinched) terminal end. Both patterns of oyster fork are shown and named in an 1898 Christofle company catalogue.
Your pictures look blurry on my monitor, but if you check the link below you’ll be able to compare the marks on your fork with the chronology of Christofle marks:
http://www.925-1000.com/a_christofle.html