Being that it is numbered and has hallmarks I would think silver not plated.Reproduction being on it could simply be that the style wasn't their design so couldn't market it as Sheffield or maybe it is reproduction of a Sheffield design.Could be either way?
The markings are from the Forbes Silver Co. (it's their initials, rather than hallmarks). The number is the pattern number.
While there are sterling Sheffield Reproduction pieces, I don't believe Forbes made any of them (several makers made these).
Sheffield (the town) produced sterling items but they would be marked with the appropriate British hallmarks.
Original "Sheffield plate" is collectible.