Hi! Beautiful set. Fortunately/unfortunately you have a nice set of Noritake made by the Morimura Brothers (A New York distributing company). The reason that said is they made hundreds and hundreds of patterns that weren't marked. "Made in Japan" was designated for imports in 1920. and the M in the center was used until 1945. So that is the window of when yours was designed.
Your best best, if someone doesn't recognize it right away on here, it to go to Replacements LTD and let them help identify your set. Let them know that you have this set and that you are interested in identifying the pattern because you register for notifications if they ever have pieces come in of the pattern...because you wish to add to your set! This is a service they offer free for people who want to add to their sets!