The letter P in ℗ stands for phonogram,[2][3] the legal term used in most English-speaking countries to refer to works known in U.S. copyright law as "sound recordings".
[5] The symbol first appeared in the Rome Convention for the Protection of Performers, Producers of Phonograms and Broadcasting Organisations, a multilateral treaty relating to copyright, in 1961.
Article 11 of the Rome Convention provided:[6] If, as a condition of protecting the rights of producers of phonograms, or of performers, or both, in relation to phonograms, a Contracting State, under its domestic law, requires compliance with formalities, these shall be considered as fulfilled if all the copies in commerce of the published phonogram or their containers bear a notice consisting of the symbol ℗, accompanied by the year date of the first publication, placed in such a manner as to give reasonable notice of claim of protection...When the Geneva Phonograms Convention, another multilateral copyright treaty, was signed in 1971, it included a similar provision in its Article 5:[7] If, as a condition of protecting the producers of phonograms, a Contracting State, under its domestic law, requires compliance with formalities, these shall be considered as fulfilled if all the authorized duplicates of the phonogram distributed to the public or their containers bear a notice consisting of the symbol ℗, accompanied by the year date of the first publication, placed in such manner as to give reasonable notice of claim of protection...The symbol was introduced into United States copyright law in 1971, when the US extended limited copyright protection to sound recordings.
The United States anticipated signing onto the Geneva Phonograms Convention, which it had helped draft.
That section provides for the a non-mandatory copyright notice on sound recordings:[13] The symbol has a code point in Unicode at U+2117 ℗ SOUND RECORDING COPYRIGHT, with the supplementary Unicode character property names, "published" and "phonorecord sign".