  It is pointed out that the previously suggested interpretation of the
hidden-charm pentaquarks $P_c(4312)$, $P_c(4440)$ and $P_c(4457)$ as molecular
bound states of $\Sigma_c \bar D$ and $\Sigma_c \bar D^*$ baryon-meson pairs
gives rise to specific relations for their decays. In particular, the heavy
quark spin symmetry predicts ratios of rates of decays of each of the molecules
to $J/\psi p$ and to $\eta_c p$ as well as of the decays to $\Lambda_c \bar D$
and to $\Lambda_c \bar D^*$. Experimental studies of these relations would thus
provide an indicative probe of the molecular structure.
