  We show that the longitudinal beam polarization option at a future
electron-positron collider provides an unambiguous distinction between
low-scale seesaw models of neutrino mass. This is possible due to the fact that
the pair production cross section of the heavy neutrinos in seesaw models is
sensitive to the polarization of the initial lepton beams, and for a suitable
choice of the polarization, shows a clear enhancement over the unpolarized
cross section. More interestingly, the choice of the beam polarization for
which the enhancement is maximum is governed by the size of the light-heavy
neutrino mixing parameter. We also find that using this effect, one can probe a
previously uncharted parameter space of the left-right seesaw model, which is
complementary to the existing searches at both energy and intensity frontiers.
