  The inhomogeneous ionization state of the universe when the first sources of
ionizing radiation appeared should lead to anisotropies in the polarization of
the cosmic microwave background. We use cosmological simulations of the process
by which the first sources ionized the intergalactic medium to study the
induced polarization anisotropies. We find that the polarization anisotropies
have rms of order ~0.01 \mu K, and local peak values of ~0.1 \mu K, smaller
than those due to gravitational lensing on small scales. The polarization
direction is highly coherent over degree scales. This directional coherence is
not expected from either primary anisotropy or gravitational lensing effects,
making the largest signals due to inhomogeneous ionization relatively easy to
isolate, should experiments achieve the necessary very low noise levels.
