See also 1c, 2b, and 2c. No. 2 represents a Japanese company, and Nos. 3 and 4 are thought to be Japanese as well, though I have no evidence of that yet.
See also 5b; Walter Del Pellegrino suggests that this mark denotes the importer rather than the manufacturer. Regarding mark #6, gotheborg.com notes that it is similar to, but is not, one of Noritake's marks and seems to be of post-WWII date, possibly the 1960s.