Symbol above others

I'd prefer using >0 and <0 rather than plus and minus signs. In my opinion insisting on + meaning positive and − meaning negative has the consequence that some students believe that −a denotes a negative quantity.

\documentclass{article}
\usepackage{amsmath}

\newcommand{\POS}[1]{\overset{>0}{#1}}
\newcommand{\NEG}[1]{\overset{<0}{#1}}

\begin{document}

\[
1\POS{(1+3)}\NEG{(1-4)}\NEG{(1-2)}>0
\]

\end{document}

For your format:

\documentclass{article}
\usepackage{amsmath}

\newcommand{\POS}[1]{\overset{\textstyle+}{#1}}
\newcommand{\NEG}[1]{\overset{\textstyle-}{#1}}

\begin{document}

\[
1\POS{(1+3)}\NEG{(1-4)}\NEG{(1-2)}={+}
\]

\end{document}

I would not write the right hand side like that.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
$1\overbrace{(1+3)}^{+}\overbrace{(1-4)}^{-}\overbrace{(1-2)}^{-}=\overbrace{12}^{+}$
\end{document}