Look on the left side of the receiver.

or find the import stamp if there is one, it will usually show nationality.
The most common:
Late Russians have no date or arsenal on the cover, these would have a Tula star on the receiver side.
A Romanian will have a Cugir arrow in a triangle on the side with a date.
An Albanian will have just a serial number, with no prefix or suffix, and a year date, or really rare, a no date. No factory stamp was used by them.
A Yugo will have just a serial, no factory stamp either.
A Chinese, that can range from just a serial number to Chinese characters with numbers, a vast amount of factory stamps was used, usually in a triangle, oval or in brackets.
A picture of the left side of the receiver is usually all thats needed. All though full pictures are always appreciated.
