Tom of rules for Nippon, Japan and made in japan marking

when Japanese marking Nippon. Japan, made in Japan
Japanese early pottery or porcelain pieces had back stamp markings consisting of the traditional Japanese "Kanji" characters for "Nippon" (the Japanese name for Japan), as well as the word "Nippon" spelled out in English.
rule of thumb Summary:
1891-1921 Nippon
The practice began in 1891 in response to the U.S. McKinley Tariff Act, which forbade the import of items that weren’t “plainly marked, stamped, branded, or labeled in legible English words.” Nippon is the English spelling of a pronunciation of what Americans call Japan.
After 1921 Japan
The Nippon mark was in use until 1921, when U.S. customs laws required Japanese importers to substitute the word "Japan" instead.  but in 1921, the word was ruled Japanese in origin, so Nippon was no longer accepted by U.S. Customs Agents.
after WWII - after 1945 Made in Japan
mostly "made in Japan" came after WWII (1912 - 1945)
information source
http://www.ehow.com/how_8160294_date-nippon-marks.html
http://www.collectorsweekly.com/asian/nippon-porcelain
http://www.japan-guide.com/e/e2129.html