  Sneutrino-antisneutrino mixing occurs in a supersymmetric model where
neutrinos have nonzero Majorana masses. This can lead to the sneutrino decaying
into a final state with a "wrong-sign charged lepton". Hence, in an $e^-
\gamma$ collider, the signal of the associated production of an
electron-sneutrino and the lighter chargino and their subsequent decays can be
$e^- \gamma \to e^+ {\tilde \tau}_1^- {\tilde \tau}_1^- + \mpT$ where the
${\tilde \tau}_1$s are long-lived and can produce heavily ionizing charged
tracks. This signal is free of any Standard Model background and the
supersymmetric backgrounds are small. Such a signal can be experimentally
observable under certain conditions which are possible to obtain in an
anomaly-mediated supersymmetry breaking scenario. Information on a particular
combination of the neutrino masses and mixing angles can also be extracted
through the observation of this signal. Possible modifications in the signal
event and the accompanying Standard Model background have been discussed when
the ${\tilde \tau}_1$s decay promptly.
