Horace is right, the cloud icon refers to the matching function (or a part it, since there are rumor to introduce a matching function for Music currently not available through xbox-music).
The Note icons means, this is music you own and which is stored on your device, whereas the radio-icon stands for music you've added through music-pass on a device (so it's part of your music), but you have no stored copy on any device.
No icon is for music you have added on your device though music-pass but haven't been downloaded.