Sansa clip interface - solid "dot"

Recently a solid “dot” appeared on the interface of the Sansa clip, along with the usual icons (shuffle, etc).  Anybody know what this dot is for?

It means you have DRM-protected tracks, and that the status of the license for those tracks is good. As the license gets closer to expiring, it’ll change to a half-full circle, and finally to an emtpy circle.