That stamp was done in the middle of the 84-94 Chinese SKS import window. At that time, the rules were unclear whether or not a 'manufacturer' was required to be stamped or whether the country of manufacture was sufficient. Later stamps that show 'CGA', 'Polytech', or 'Norinco' came after the rules were clarified and it was understood what information had to be stamped during import in addition to 'China'. You also see the transitions in locations of the markings (from hidden areas to visible areas anywhere and finally to visible areas on the receiver or barrel only), as well as types of stamps (hand engravings, minimal chemical etchings, to stamps, mechanical engravings, and laser etchings), and size of characters (from tiny almost unreadable characters to the current standard of at least 1/16" tall).