  We point out that polarization measurements such as the longitudinal fraction
and the transverse left-right asymmetry in the Bauer-Stech-Wirbel (BSW) class
III processes involving two final vector mesons, $B^- \ra \rho^- {D^*}^o$ taken
as an example, are useful in determining the relative sign as well as the
relative magnitudes of the coefficients $a_1$ and $a_2$.
