XG2CX

The operator claims operations from: Germany, Lithuania, Latvia, Estonia, Finland.
There is no operator name or address and the reverse side is blank.
I do have a couple of cards on the site from G2CX, Douglas Chisholm dated 1929 & 1975.
I think G2CX worked for a diplomatic service, the X is just for portable.
This came with a stack of cards from the 1920's and 1930's.

QSL courtesy of G3NDC
Info courtesy of G4UZN