What is this mark on a "silver" spoon ?

[LadyEloise1]

My grand aunt gave me some old spoons she had. They are silver coloured and have Wm Rogers and separately the letters IS stamped on the underside of the handle.
I presume they are silver plated.
Does anyone know what the IS means please ?

A very quick Google says it stands for International Silver who own Wm Rogers
https://www.precious-metal-refining.info/1847-rogers-brothers-is-silver-value-precious-metal-refining-blog/#:~:text=This%20is%20the%20founding%20date,has%20owned%20Rogers%20since%201898.

Thank you

@LadyEloise1 I didn't realise you were born with a silver spoon in your mouth

I think they're only silver plated, more Hyacinth Bucket than aristo @JaneJeffer
The spoons I mean not me. 😀

Hello it’s me, Hyacinth 😆

If they’re plated they’ll have a mark like “EPNS”

Hyacinth would keep the EPNS for when Elizabeth called round for coffee