I really liked #160 sollution, but I would change that icon to something more like the "shelf" icon on Mac or a "menu-like icon" similar to the one of LIM (without the triangle symbol inside).
Also to give the idea of "toggling", the "bubble" of the icon could look like "pressed" when activated (when the menu is visible) and look like as an unpressed button when disabled (not visible)
I really liked #160 sollution, but I would change that icon to something more like the "shelf" icon on Mac or a "menu-like icon" similar to the one of LIM (without the triangle symbol inside).
Also to give the idea of "toggling", the "bubble" of the icon could look like "pressed" when activated (when the menu is visible) and look like as an unpressed button when disabled (not visible)