Today I tested suggested patch on an 10.11 and on 10.6.8.

The good news is that, visually, the patch looks really good! It replaced the boring black square with the standard OS X icon "Caution" icon -- an exclamation mark on a triangle. It is less intrusive, which I consider a good thing.

Unfortunately, the code doesn't compile under 10.6.8. The code use the "hidden" property of NSView (introduced in 10.10), and it the compiler complains about the "." in the "[BellView.instance ..." construct.

I notices a minor problem under 10.11 as well. The icon is shadowed by scroll bars, if they happen to be displayed in the middle of the frame, like when having two side-by-side windows.

I will make an attempt to rewrite to code to work under 10.6.8.

Sincerely,

    Anders Lindgren