% k4\e
\begin{scope}[every node/.style={circle,draw}]
\node (1) at (0,1) {$1$};
\node (2) at (1,1) {$2$};
\node (3) at (1,0) {$3$};
\node (q) at (0,0) {$q$};
\end{scope}
% positive edges
\begin{scope}[every node/.style={draw=black},
every edge/.style={draw=black}]
\path (1) edge (q);
\path (3) edge (q);
\end{scope}
% negative edges
\begin{scope}[every node/.style={text=red,font=\bfseries},
every edge/.style={draw=red}]
\path (1) edge node[above] {$-$} (3);
\path (3) edge node[right] {$-$} (2);
\path (1) edge node[above] {$-$} (2);
\end{scope}
