After its defeat in World War II, Japan was occupied by U.S. forces. Ceramics made between 1945 and 1952, when occupation ended, was typically stamped "Occupied Japan" or "Made in Occupied Japan," possibly to reassure U.S. buyers that some of the money would be used to pay reparations. There was still some strong anti-Japan sentiment at the time, and pottery makers likely hoped the "occupied" stamp would help them overcome that.
Learn about Occupied Japan and the associated markings by reading through a website such as OccupiedJapan.net and checking out the extensive photographic library of Occupied Japan markings, arranged by manufacturer, on The 4 Cs website (see Resources).
Search for "Occupied Japan" items on online auction sites for further study. The more familiar you are with the many types of ceramics that were made for export in Japan in the post-World War II years, and the "occupied" markings somewhere on them, the better you'll be able to identify them when you see them for sale.
Pay a visit to the nearest antique mall that carries antique Japanese pottery. Inspect each piece with a magnifying glass and check to see if the piece says either "Made in Occupied Japan" or "Occupied Japan." If it doesn't, it may not have been made for export to the United States during the 1945 to 1952 time frame.