Looking to identify MK4 marking

Hello. I’m attempting to identify a marking to determine if it’s silverplate and its possibly history. The marking is on the back of a tray where there is also a sticker with the name “BERIOZKA”, which I believe refers to the name of Russian shops especially set up for tourists. I believe this may be anywhere from the 60s through to the 80s and I’m presuming was purchased in (Soviet) Russia. The set consists of the small round tray and 6 goblets that seem to be silver (or gold?) on the inside but not on the outer part and decorative foot of the goblets. Most goblets bear a mark on their underside (what looks like a number) and 1 does not. Any info you could provide would be greatly appreciated.

Thanks kindly.

Forgot to add the tray picture with marking. Here it is. Any assistance with the marking is appreciated!