Right now this is an icons-only button, and those are known to have somewhat poor usability in the case where the icon used is not 100% universally recognizable (e.g. trashcan for delete, magnifying glass for search). Therefore let's try to improve the usability here by giving this button some text: "Menu", since that's what it is. A button that will open a menu.
RFC because this is a change that we would want to roll out for other instances of hamburger menus too if we do it here, and I wanted to start a discussion on whether we think that would be a good idea to do in general. But I couldn't resist doing it in code form. :)
NOTE: for those of you who hate hamburger menus, let's try to avoid suggesting removing it entirely as that is out of scope here because it would require a significant redesign to find other places for everything currently in the hamburger menu.