In 1997, David Bowie sold bonds backed by future copyright royalties on some of his songs. These royalties are income from licensing of his songs, such as royalties from public performance of his works.
These royalties can be a consistent source of income for certain artists, and they also led to something of a revolution in the bond market. Opening it up for other artists to raise funds while retaining ownership of their work, as well as bonds backed by some even stranger things, like timeshare rentals.
Registered copyrights and a strong strategy for protecting your IP can lead to increased flexibility in cash flow and generation down the line.