The history of the Shanghai Agency is quite interesting.
While other nations had overprinted their stamps for use in their post offices abroad, it wasn't until 1919 that the United States took the step. The definitive stamps of 1917-1919 were used with overprints at twice the value of the stamp being overprinted. Overprint values ranged from 2¢ to $2. Scott lists these as K1-K18. A special delivery stamp was overprinted but not put into use.
The stamps were short lived. The U.S. Postal Agency in Shanghai was closed on December 31, 1922, and was declared discontinued after it had completely closed its affairs on January 31, 1924. The stamps were on sale at the Philatelic Agency for a short time after the closure in 1922.
These stamps are from the collection of P. Lau.
