hellp identify I.M.K. porcelain

Hello Magnolija, have to disappoint you, I do not know the answer. The letters are definitely from the Russian alphabet. So, it cannot be German. You say this is more than 100 years old, at that time Latvia used the alphabet which looked more like Latin (but with some particular letters)/ So, does not look like Latvian. Now, we have Russian. I did not find that mark in the catalogues of imperial Russian porcelain. To me it looks like the abbreviation of family name, name, and patronymic of the owner. Probably the set was made at the order and they put the initials of the owner.

 

the letters are definitely German. J.M.H. , most probably 1880s to at least 1914, Fraktur that was used for printing.
sorry for intervening.

 

Yes, if you could post some close-up photos, these should be helpful.

 

I have already posted examples of the same shapes from Kuznetsov factory on Riga, they are from the 1930s. Nothing to see with 19C I am afraid

 

seems you don't know how long the scripts were in use, I'm afraid.

 

Assuming that those are not printed letters, but handwritten capital letters, the first letter which you take for J is the fourth in the first line, second letter is fourth in the third line, third is either second or fifth in the third line. These are Russian handwritten letters:

 

It could potentially be the Russian alphabet, of course, but the first letter does not look like Г, the upper line is too short.