\documentclass[border=3mm]{standalone}
\usepackage{pgfplots-autonode}
\pgfplotsset{compat=1.18}

\begin{document}
\begin{tikzpicture}
\begin{axis}[
  width=13cm,height=9cm,
  xmin=-4,xmax=4,ymin=-4,ymax=4,
  axis equal image,grid=both,
  xlabel={$x$},ylabel={$y$},
  auto node placement,
  auto node algorithm=repair,
  auto node bbox mode=oriented,
  auto node failure mode=error,
  auto node candidates=81
]
  \foreach \b in {-3,-2,...,3}{
    \addplot[blue!70!black,domain=-4:4,samples=2] {x+\b}
      \pgfplotsautonode[preferred pos=.5,sloped=true,
        node options={fill=white,fill opacity=.9,text opacity=1}]{$+$};
    \addplot[red!75!black,domain=-4:4,samples=2] {-x+\b}
      \pgfplotsautonode[preferred pos=.5,sloped=true,
        node options={fill=white,fill opacity=.9,text opacity=1}]{$-$};
  }
\end{axis}
\end{tikzpicture}
\end{document}

.