We had some time ago a discussion about the polyline icon. User are with some regularity surprised about the famous M key which makes the polyline so much more powerful. So we talked about an icon which was not only a zigzag bit had a curved line at the end. Hey Chrisb, I actually created two (but ...
Wow, here is some hierarchical discussion!
Well, here is a topic I made for Blender 2.8 considering hierarchical navigation, such as layers, groups, etc,
can be useful as entire problem overview (with pictures and descriptions)