When the artist signs a contract with the label, sometimes a separate contract is drawn up assigning copyright to the label. In normal music, usually the artist retains the composition and the label retains the sound recording. Sometimes you assign all your copyright to the label or split it with the label. Sometimes a big label can do very aggressive money making things with that copyright (like use it as a theme song to sell hamburgers with) and its a good idea to let them play with it (or not), sometimes they just want everything out of you they can get. In most underground label situations, the label just collects all the money it can get and gives the artist a much higher cut of the actual sale price of the record (Artist Royalty). Often, no-one is really trying to collect money from BMI ASCAP etc. because they figure there just isn't any money there. But there often is, primarily because of european airplay.