By default, Latex uses parentheses to bracket equation numbers (i.e.,
to the right of each equation). To use square brackets, put this syntax
toward the beginning of your document:
\makeatletter
\def\@eqnnum{{\normalfont\normalcolor[\theequation]}}
\makeatother
Obviously, you could riff off of this to make other formatting changes to the equation labels.
Last modified: 12/22/09.