  It is shown that the relative sign between the $NN\omega$ and $\pi\rho\omega$
coupling constants can be determined most sensitively from $\omega$ production
processes in $NN$ collisions. Recent data on these reactions clearly favor the
sign of the $\pi\rho\omega$ coupling constant which is opposite to that
inferred from studies of the photoproduction reaction in combination with the
vector meson dominance assumption and used by many authors. Implication of this
finding in the description of other reactions is discussed.
