  We study the signal of cosmic string wakes present before the time of
reionization in the cross-correlation signal of 21-cm redshift and B-mode CMB
polarization maps. The specific non-Gaussian signal of strings in the position
space cross-correlation maps can be extracted by means of a matched filtering
analysis. Signals of strings with tension somewhat lower than those
corresponding to the current upper bound can be identified when embedded in a
background of Gaussian fluctuations from a Planck best-fit LCDM model.
