  Polarization quasi-probability distribution (PQPD) is defined in the Stokes
space, and it enables the calculation of mean values and higher-order moments
for polarization observables using simple algebraic averaging. It can be
reconstructed with the help of polarization quantum tomography and provides a
full description of the polarization properties of quantum states of light.
  We show here that, due to its definition in terms of the discrete-valued
Stokes operators, polarization quasi-probability distribution has singularities
and takes negative values at integer values of the Stokes observables. However,
in experiments with `bright' many-photon states, the photon-number resolution
is typically smeared due to the technical limitations of contemporary
photodetectors. This results in a PQPD that is positive and regular even for
such strongly nonclassical states as single-photon seeded squeezed vacuum.
  This problem can be solved by `highlighting' the quantum state, that is, by
adding a strong coherent beam into the orthogonal polarization mode. This
procedure bridges polarization quantum tomography with the Wigner-function
tomography, while preserving the main advantage of the first one, namely,
immunity to the common phase fluctuations in the light path. Thus, it provides
a convenient method for the verification of bright nonclassical states of
light, such as squeezed Fock states.
