New TiKZ 3.0 pics
can help you:
\documentclass[tikz,border=2mm]{standalone}
\usetikzlibrary{positioning}
\tikzset{mysymbol/.pic={
\node[circle,draw,thick,inner sep=0pt, minimum size=2ex] (-sum) {};
\draw[semithick] (-sum.north west)--(-sum.south east);
\draw[semithick] (-sum.south west)--(-sum.north east);
\fill (-sum.center)--(-sum.south west) arc (-135:-35):1ex)--cycle;
}}
\begin{document}
\begin{tikzpicture}
\node (a) {A};
\path pic (symbol_a) at ([xshift=1cm]a) {mysymbol};
\pic[above right=5mm and 8mm of a, red] (symbol_b) {mysymbol};
\pic[left=of symbol_b-sum, blue] {mysymbol};
\end{tikzpicture}
\end{document}

Some pic
examples here:
Update: Include filled sectors as parameter
Next code show one possibility of including which sectors will be filled as a parameter to the pic
definition.
To use parameters
with a pic
a new syntax is needed, the original mysymbol/.pic
changes to pics/mysymbol/.style={code={...
. This is enough with only one parameters but it's also possible to use 2 (pics/mysymbol/.style 2 args={code={...
) or more (pics/mysymbol/.style n args={n}{code={...
). Take a look at TikZ 3.0---Multiple arguments for `pic` for some other examples.
In this case you can pass a sector list (from 0 to 3, 0=east sector, 1=north, ...).
\documentclass[tikz,border=2mm]{standalone}
\usetikzlibrary{positioning}
\tikzset{
pics/mysymbol/.style={
code={
\node[circle,draw,thick,inner sep=0pt, minimum size=2ex] (-sum) {};
\draw[semithick] (-sum.north west)--(-sum.south east);
\draw[semithick] (-sum.south west)--(-sum.north east);
\foreach \i in {#1}
\fill[rotate=90*\i] (-sum.center)--++(-45:1ex) arc[start angle=-45,delta angle=90,radius=1ex]--cycle;
}}}
\begin{document}
\begin{tikzpicture}
\node (a) {A};
\path pic (symbol_a) at ([xshift=1cm]a) {mysymbol={2,0}};
\pic[above right=5mm and 8mm of a, red] (symbol_b) {mysymbol={0}};
\pic[left=of symbol_b-sum, blue] {mysymbol={0,2,3}};
\end{tikzpicture}
\end{document}
