  We study the behavior of the Hall coefficient, $R_H$, in a system exhibiting
$d_{{x^2}-{y^2}}$ density-wave (DDW) order in a regime in which the carrier
concentration, $x$, is tuned to approach a quantum critical point at which the
order is destroyed. At the mean-field level, we find that $n_{\rm Hall}=1/R_H$
evinces a sharp signature of the transition. There is a kink in $n_{\rm Hall}$
at the critical value of the carrier concentration, $x_c$; as the critical
point is approached from the ordered side, the slope of $n_{\rm Hall}$
diverges. Hall transport experiments in the cuprates, at high magnetic fields
sufficient to destroy superconductivity, should reveal this effect.
