This is a weakaura to show when you have queued Heroic Strike or Cleave.
It also shows a recommendation when to use Heroic Strike (Above 24 rage, or if the cooldown on BT is greater than 4 seconds)
These are recommendations when I simmed the abilities using the Guybrush sim. I have improved heroic strike (you should change it if you don't to 30 rage) and I'm not so sure about the 4 second cooldown on BT. Going to play with it a bit, but this is a good starting point.
(I have down mouse wheel as my heroic strike keybind)