We report a unique set of photometric and polarimetric observations made by the imaging photopolarimeter aboard the Pioneer spacecraft shortly after it penetrated the ring plane from above on its way to closest approach. The bright planet limb is observed through the rings, which themselves weakly reflect direct sunlight. Polarizations range from 41% (16%) at the extreme planet limb to 2% (1.5%) at the darkest part of the B ring in the blue (red) channel. Detailed structure of the A ring is evident, most notably the Encke gap.