In Map views, Tinderbox uses a 'dog-ear' (like the folded page corner) to denote the presence of content; Outline view uses a different method, with content-related variable note icons.
The dog-ear is not interactive, it simply indicates that a note has content. In Map and Treemap views, the dog-ear is bottom right of the note icon, in Charts it is at bottom left of the note icon.
The background colour of the dog-ears is the same variable colour used for outline icons to indicates the age of the note (since last edit). Originally, the background colour of the dog-ear was the view's background colour.