
\documentclass[12pt]{article}
  \usepackage{tikz}
  \pagestyle{empty}
  \setlength{\parindent}{0pt}

\begin{document}
$ N = (-\tikz[overlay]\draw[red] (0pt,2ex) -- ++(0ex,-8.5ex);9) + (+\tikz[overlay]\draw[red] (0pt,2ex) -- ++(0ex,-8.5ex);5) $

$ N = \phantom{(}\mathord{-}9\phantom{)} + \phantom{(}\mathord{\phantom{+}}5\phantom{)} $

$ N = \phantom{(}{-}9\phantom{)} + \phantom{({+}}5\phantom{)} $
\end{document}
