Things You'll Need
Instructions
Look for the word ̶0;Nippon̶1; written anywhere on the stamp (looks like a capital "E" with an extra, vertical line running down the right side.) Most stamps made in post-1947 Japan bear the name of the country in roman script.
If you cannot find the word ̶0;Nippon̶1; on the stamp, check for any logographic (̶0;picture̶1;) writing. If the stamp does bear any logographic writing, it is likely Chinese style script (called ̶0;kanji̶1;), which is used in China and Japan.
Look for one of two kanji characters. One Is a box, long sides up, with a horizontal line cutting it in half (likely made in Japan after 1947). The other is a box, long sides horizontal, with a vertical line running through it (likely made in China).
Search the stamp for a chrysanthemum. (Search online for a picture if you don't know what this flower looks like.) The Japanese imperial chrysanthemum is a stylized circle with 16 petals radiating out from a smaller circle in the center. If the stamp bears this crest, it was likely issued in Japan prior to 1947.