Probably not much help, but try here:
http://bluejacket.com/usn-usmc_ww2_...n-codes.html ... or here:
http://www.patriotfiles.com/index.p...=1108&page=1 both suggest [FPO NY?] 930 (if it is in fact an FPO) is Kunming China.
Another possibility
(My GUESS) is that the cover is from the document signing ceremony aboard the USS Missouri based on the comment at the bottom of the cover and the date - 2 Sep 1945, in which case 930 might be a time stamp.
According to Wikipedia: "The formal surrender occurred on September 2, 1945
around 9 a.m. Tokyo time, when representatives from the Empire of Japan signed the Japanese Instrument of Surrender in Tokyo Bay aboard the USS Missouri." So "930" could be right after the event concluded.