We can only assume that the "P.M." stood for "Porzellan-Malerei" or "Porzellan-Manufaktur", as no further information could be found in any mark reference book.

M050316a
Crown above shield with initials "P.M." and crossed swords, all above "CW".

M050316b
Crown above shield with initials "P.M." and crossed swords, all above "BAVARIA" and "GERMANY".