On the determination of the relative sign of $a_1$ and $a_2$ from polarization measurements in $B^- \rightarrow \rho^- {D^*}^o$ decay

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 $a_2$.