Otagiri Manufacturing Company, more commonly called OMC, was formed @1954.
As a Japanese Trading Company, all products by Otagiri were manufactured in Japan. However, Otagiri imported wares from many Japanese kilns/companies. Most were marked with an OMC sticker. However some were produced especially for Otagiri. Some were better marked than others.
Slight differences one sometimes sees in the same model OMC mug from the same period are due to the different Japanese manufacturers OMC used all producing their own molds.
They had home offices in Tokyo and Nagoya, Japan. Their US shipping headquarters were based out of both San Francisco (1400 Folsom St.) and New York (11 East 26th St.), but they had offices/showrooms in other locations, including in Los Angeles, Chicago, Dallas, Seattle, Coral Gables (Florida), and Honolulu (Hawaii).
Around the 1960s, a very similar company called Jard Products arose that had the same designs and even nearly identical stickers.
In 1994, Otagiri was sold to Enesco Corporation, a division of Stanhome.
Enesco, which now owns the rights to the designs, has not opted to start producing them again.