  If the disappearance of the broad emission lines observed in changing-look
quasars originates from the obscuration of the quasar core by dusty clouds
moving in the torus, high linear optical polarization would be expected in
those objects. We then measured the rest-frame UV-blue linear polarization of a
sample of 13 changing-look quasars, 7 of them being in a type 1.9-2 state. For
all quasars but one the polarization degree is lower than 1%. This suggests
that the disappearance of the broad emission lines cannot be attributed to dust
obscuration, and supports the scenario in which changes of look are caused by a
change in the rate of accretion onto the supermassive black hole. Such low
polarization degrees also indicate that these quasars are seen under
inclinations close to the system axis. One type 1.9-2 quasar in our sample
shows a high polarization degree of 6.8%. While this polarization could be
ascribed to obscuration by a moving dusty cloud, we argue that this is unlikely
given the very long time needed for a cloud from the torus to eclipse the broad
emission line region of that object. We propose that the high polarization is
due to the echo of a past bright phase seen in polar-scattered light. This
interpretation raises the possibility that broad emission lines observed in the
polarized light of some type 2 active galactic nuclei can be echoes of past
type 1 phases and not evidence of hidden broad emission line regions.
