  Electric signals have been recently recorded at the Earth's surface with
amplitudes appreciably larger than those hitherto reported. Their entropy in
natural time is smaller than that, $S_u$, of a ``uniform'' distribution. The
same holds for their entropy upon time-reversal. This behavior, as supported by
numerical simulations in fBm time series and in an on-off intermittency model,
stems from infinitely ranged long range temporal correlations and hence these
signals are probably Seismic Electric Signals (critical dynamics). The entropy
fluctuations are found to increase upon approaching bursting, which reminds the
behavior identifying sudden cardiac death individuals when analysing their
electrocardiograms.
