Hi! Cool plate! I'd love to see the other side as well if you have a picture handy.

'19 гр' means 19 grams, so I'd imagine if you weighed the plate you'd find it to weigh about that much.

'ЛФЗ' means Ленинградский Фарфоровый Завод or Leningrad Porcelain Factory. You'll see the same logo at the bottom of that page I've linked there. It was started during the Imperial Period and continued production during the Soviet Period as well. This is the premier porcelain producer in Russia (and still works today), so it's of quite high quality most likely.

I can't tell you what the '2 C' means with any confidence unfortunately but I'd hazard a guess (and part of the reason I asked to see the obverse side of the plate) that it likely refers to the number of carats of gold leaf used on the face. That's not an entirely brilliant hypothesis because carat in Russian is карат, however for most measurements and other internationally used things like license plates, Russia and the Soviet Union uses/used Latin letters so it's not entirely improbable. It could also be '2 серия' or second series, but at this point, like I said, I'm just guessing.