When considering system

\begin{equation*}

\mathbf{x}'=A\mathbf{x} \qquad \text{with } \

A=\begin{pmatrix} a & b \\ c & d\end{pmatrix}

\end{equation*}

and discovering that it has two adjoint complex (not real) eigenvalues $\lambda_\pm =\mu \pm i\nu$, one should not only tell, if it is an unstable ($\mu>0$) or stable ($\mu <0$) focal point, or a center ($\mu =0$), but also the direction of rotation.

Observe that, $\lambda_\pm$ are roots of the equation $\lambda ^2- (a+d)\lambda + ad -bc=0$ with the discriminant $D:=(a+d)^2-4(ad -bc))=(a-d)^2+4bc$, and we consider the case $D<0\implies bc <0$. Thus $b$ and $c$ are not $0$ and have opposite signs.

Then, if $b<0$ (and $c>0$) rotation is counter-clockwise, and if $b>0$ (and $c<0$) rotation is clockwise.