  We collected optical and near IR linear polarization data obtained over
20--30 years for a sample of 51 blazars. For each object, we calculated the
probability that the distribution of position angles was isotropic. The
distribution of these probabilities was sharply peaked, with 27 blazars showing
a probability < 15% of an isotropic distribution of position angles.
  For these 27 objects we defined a preferred position angle. For those 17 out
of 27 blazars showing a well-defined radio structure angle (jet position angle)
on VLBI scales (1--3mas), we looked at the distribution of angle differences --
the optical polarization relative to the radio position angles. This
distribution is sharply peaked, especially for the BL Lac objects, with
alignment better than 15 degrees for half the sample. Those blazars with
preferred optical position angles were much less likely to have bent jets on
1--20mas scales. These results support a shock-in-jet hypothesis for the jet
optical emission regions.
