I've made little superscript plus and minus signs for something by defining
\newcommand{\minus}[1]{{#1}^{\scalebox{0.8}{-}}}
\newcommand{\plus}[1]{{#1}^{\scalebox{0.6}{\!+}}}
the problem is that compared to the plus, the minus looks really heavy. See for yourselves:

I think I'd rather have a heavier plus. Any thoughts? (other than that I should be less anal)
\newcommand{\minus}[1]{{#1}^{\scalebox{0.8}{$-$}}}– Joseph Wright Jul 07 '12 at 15:27\scaleboxIf you had just use \pi^- and \pi++ they would naturally be smaller size from teh scriptstyle font. By using a box command you go out of math mode so back to text size and then have to shrink by hand. – David Carlisle Jul 07 '12 at 16:03