  Extending the Kaiser-Stebbins mechanism we propose here a method for
detecting relics of topological defects such as cosmic strings based on
lens-induced small-scale B-type polarization in the CMB. Models of inflation,
in which large scale structures of the Universe emerge from the inflaton
fluctuations,do not exclude the formation of topological defects at the end of
the inflationary phase. In such case, we show that the lens effect of a string
on the small scale E-type polarization of the CMB induces a significant amount
of B-type polarization along the line-of-sight. The amplitude of the effect is
estimated for different resolutions of CMB experiments.
