  After the submission of the paper, three strong earthquakes with magnitude
around 6.0-units occurred on October 17 and October 20, 2005, with epicenters
in the Aegean Sea, at a distance {\em only} 100km from MYT station at which the
intense signals $M_1$ to $M_4$ -analyzed in the main text- have been recorded.
This confirms experimentally the proposed criterion we used for the
classification of these signals as Seismic Electric Signals (SES). Moreover, we
show that, if we follow the procedure described in [P.A. Varotsos, N. V.
Sarlis, H. K. Tanaka and E. S. Skordas {\it Phys. Rev. E} {\bf 72}, 041103
(2005)], the analysis in the natural time of the seismicity after the SES
initiation allows the estimation of the time window of the impending
earthquakes with very good accuracy.
