The Post Exchange (or PX) facilities are trading posts located in bases of the US Army or US Air Force, and operated by the Army & Air Force Exchange Service. Equivalent facilities in bases of the US Navy are called Naval Exchange.
Many Japanese products (not only cameras) sold in the US military bases in Japan were stamped with special markings. The rumour says that the products sold in the PX shops were not subject to the same taxes as those sold in Japan's domestic market, and that the markings were applied to avoid tax evasion.
The earliest marking, used around 1948–49, is a diamond-shaped engraving containing the Roman letters CPO or their katakana equivalent シｰピｰオｰ. "CPO" is said to stand for Central Purchasing Office, presumably a temporary office of the occupation army.
The "CPO" marking was soon replaced by an EP marking inside a diamond, either in black or in red. The exact meaning of the letters "EP" is not confirmed; they probably don't stand for "Exchange Post", because the facilities were called the reverse, and a more plausible candidate is "Export Permitted". The EP marking was perhaps applied until the early 1970s.
Latin or Katakana <Katakana> marked <CPO> <EP> was the normal engraving during the C.P.O. office period of US Allied Army Occupied Japan 1947-1950 or M.I.O.J. to some. <Katakana> is a very rare mark, which says in Japanese <C.P.O.> and the camera was made only for Export production and was NOT too be Taxed! You can think of it as = to the <EP> mark = Export Production, Not the often referred to incorrectly stated on eBay & other web sites as, thinking Exchange Post, or military store; which is really called Post Exchange! Truth be told all <EP> marked cameras were also sold in Military base stores world-wide , ordered by the C.P.O. division of US military occupied Japan, because they were NOT too be Taxed! That said <EP> products of all kinds of optics and metals, were also Exported without taxation to other areas of the world. The point here is <EP> marked cameras were not only sold in just military bases. <CPO> was the earlier 1947, 1948 marking and <EP> the later marking. <Katakana> C.P.O. is extremely rare, and those cameras so marked command respect and higher prices! Regards, Don
- Dechert, Peter. Canon Rangefinder Cameras 1933–68. Hove, East Sussex: Hove Foto Books, 1985. ISBN 0-906447-30-5.