  We investigate the effect of a mirror-symmetry plane in multiple-scattering
media under plane-wave illumination along the symmetry plane. Designed and
fabricated samples' optical transport properties are compared quantitatively
with three-dimensional modeling. Strong polarization-dependent deviations of
the bulk speckle-averaged intensity distribution at the symmetry plane are
observed, showing either up to a factor two enhancement or complete suppression
of the ensemble-averaged intensities. We derive analytical expressions for the
ensemble-averaged intensity profiles near the symmetry plane. Apart from their
interest in fundamental light propagation studies, applications of
mirror-symmetric scattering media are envisioned in anti-counterfeiting.
