I guess we can continue this discussion here. It comes around every four or five years, and there are lots of new faces.
Here are a couple keys for Japan. The figure-8/snowman on the right is always Japan. The chrysanthemum symbol on the left is Japan, too.

The chrysanthemum should always have 16 petals. Earlier forgeries of classic Japan sometimes missed this detail, and the number of petals varied.
Note that if the middle bar of the figure-8 doesn't touch the sides, then you're dealing with a Japan
prefecture stamp:

Here is the 12-pointed sun found on Republic of China stamps:

(This will be Republic of China, not communist China.)
Slightly related is the orchid crest of Manchukuo:

If you see this, it's Manchukuo, but it's not found on
all stamps of Manchukuo.