Is it definitely silver plated? One of the marks appears to have the word 'Etain' (French for Pewter). The quality marks for Etain are often expressed as 0.950 or 95% or similar, and this is what appears, to me, to be stated above the word 'Etain'.
The item gives a blood red response to silver testing acid, almost as if it were solid silver. However, under the plating the acid turns blue then black, similar to other white metal plated pieces. I suppose it could be plated pewter.