From the graph:
- For $x = 2$, $f(2) = -1$.
- For $x = -2$, $f(-2) = 1$.
Clearly, $f(2) = - f(-2)$. Similarly for other symmetric points: $f(3) = - f(-3)$.
This is the definition of an odd function:
\[
f(x) = -f(-x) \quad \forall x
\]
Thus the correct option is (3).
\[
\boxed{f(x) = -f(-x)}
\]