  Magnetic fields play essential roles in protoplanetary disks. Magnetic fields
in the disk atmosphere are of particular interest, as they are connected to the
wind-launching mechanism. In this work, we study the polarization of the light
scattered off of magnetically aligned grains in the disk atmosphere, focusing
on the deviation of the polarization orientation from the canonical azimuthal
direction, which may be detectable in near-IR polarimetry with instruments such
as VLT/SPHERE. We show with a simple disk model that the polarization can even
be oriented along the radial (rather than azimuthal) direction, especially in
highly inclined disks with toroidally dominated magnetic fields. This
polarization reversal is caused by the anisotropy in the polarizibility of
aligned grains and is thus a telltale sign of such grains. We show that the
near-IR light is scattered mostly by $\mu$m-sized grains or smaller at the
$\tau=1$ surface and such grains can be magnetically aligned if they contain
superparamagnetic inclusions. For comparison with observations, we generate
synthetic maps of the ratios of $U_\phi/I$ and $Q_\phi/I$, which can be used to
infer the existence of (magnetically) aligned grains through a negative
$Q_\phi$ (polarization reversal) and/or a significant level of $U_\phi/I$. We
show that two features observed in the existing data, an asymmetric
distribution of $U_\phi$ with respect to the disk minor axis and a spatial
distribution of $U_\phi$ that is predominantly positive or negative, are
incompatible with scattering by spherical grains in an axisymmetric disk. They
provide indirect evidences for scattering by aligned non-spherical grains.
