peter Not sure which way you were thinking - as for UI positioning of said button/feature, but I think it would make sense either next to the "SORT BY" and "FILTER" options at the top after hitting edit....
OR
At the bottom where you have the "add to playlist" "new playlist" "select all" etc.
I would say that it might be better at the top, because it is essentially another filter option. As for an icon to display it, maybe a giant letter "K"?
I'm really excited for the number of people who will benefit from this, especially after importing all of their songs. A few of us used OnSong for a while and this is significantly better.