The P-in-a-circle symbol (akin to © and ®) indicates copyright on sound recordings. `P' originally stood for `phonograph'. For example, Tori Amos's album Little Earthquakes is © 1991 Warner Music UK Ltd. (referring to the lyrics, the music, and the packaging), but (P) 1991 WEA International Inc. (referring to the recording itself). If you cover a song without authorisation, or node the lyrics, you are violating the © copyright; if you trade the MP3, you are probably violating both.