Tyrone is right: the "P" indicated "Parlor" (Zonophone's 7" disc) while "C" denoted "Concert" (which was Zonophone's 9" disc). These names came into use after the demise of the National Gramophone Corporation in September 1901, and the reorganization of Universal into the Universal Talking Machine Manufacturing Company. This nomenclature was dropped by late 1904, when the "Universal Zonophone Record" paper label was replaced by the "Zonophone Record" label.
Back in 1983, I wrote an article on "American Zonophone Records" which appeared in Vol. VII, No.6 of the "Antique Phonograph Monthly." There are photos of various labels there. Additionally, color photos of Zonophone discs can be found on pages 131-133 of Michael Sherman's "Collector's Guide To Victor Records." George Paul
