I never noticed this before. It is in the title bar. Its a good catch by the OP. I think Pwalpwal nailed it. 
 
I did a search on this and came up empty. I did find this thread though. So as far as I am concerned the explanation of Pwalpwal is the right one until something better comes along. 

The brackets have always been there for me. The word "Track" is referring to the view you are in I think. If you undock the multidock and look at it "Track" changes to "Multidock".

Yes, the - track - is the current view.Thanks teego.
Maybe the brackets have always been there and I've just not noticed.
[Thanks again for taking the time to reply] :)

Ever since I saw [Your Music is Crap] in the title bar I have ignored it...

Isn't this just so that if you have multiple projects open, you can see which project's track window you are looking at?