  A fraction of the radiation produced by an accretion disk may be Thomson
scattered by a wind flowing away from the disk. Employing a simple
plane-parallel model of the wind, we calculate the polarization of the
scattered radiation and find that its sign depends on the wind velocity,
beta=v/c. In the case, 0.12 < beta < 0.78, the polarization is parallel to the
disk normal, i.e., it is orthogonal to the standard Chandrasekhar's
polarization expected from accretion disks. The velocity of an
electron-positron wind is likely to saturate near the equilibrium value beta_*
of order 0.5 for which the accelerating radiation pressure is balanced by the
Compton drag. Then the change of polarization by the wind is most pronounced.
This may help to reconcile the standard accretion disk model with the optical
polarimetric observations of non-blazar AGNs.
