From the end of World War II, the allied forces occupied Japan for seven years. The unofficial occupation started Aug. 14, 1945, and the occupation lasted until April 25, 1952. During these seven years, half of all Japanese exports had to be labelled as coming from "Occupied Japan."
Pieces from Occupied Japan are marked with an "OJ". This mark will be under the glaze. Since only half of the pieces required the identity mark, it is possible to get two-piece sets, such as a cup and saucer, where only one item bears the mark.
The significance of the "OJ" to a collector is that it securely identifies when a piece was produced and exported. The mark and the limited years it was produced have created a collectivity that otherwise did not exist.
Most prices on china from Occupied Japan hover around $50-$70 dollars a set for a single saucer and cup. As with all collectibles, collectors are split on whether or not these prices are appropriate. According to some, the mark raises the price too much on what would otherwise be a lower priced item. Others feel that the mark gives an authenticity and makes the item worth a higher price.
Condition plays a major role in the value of collectibles, china included. Having a matching set is imperative for the value of the set. Unbroken, unchipped pieces carry higher value then those that show damage and wear. Do not wrap your china or bisque in newsprint as the print could rub off, ruining the value of your piece.
There are frauds out on the market. If the mark is not beneath the glaze there is a high probability that the piece is a fraud. On glazed pieces you can test the mark with nail polish remover, and if the mark comes off it is a fake. Do not use this test on unglazed pieces.