The study of electromagnetic noise in the Ioannina region (NW Greece) shows the existence of long transient electric signals (duration>10 s) without measurable correlated magnetic signals, as is the case for Seismic Electric Signal (SES) observed in the VAN network of short-term earthquake prediction. Our signals have an artificial origin and are emitted by different kinds of transmitters implanted in the Ioannina region. This origin can be clearly ascertained from simultaneous observation, at stations in direct sight of the transmitters, of four electromagnetic components (two electric and two magnetic) in a broad band of frequencies (10-3-103 Hz). Relying on these observations, it is proposed that the April 18 and 19, 1995 electric signals, interpreted by the VAN group as SES precursors to the May 13 Kozani earthquake, are due to some transmitter located far to the North of the IOA station of the VAN network. The transmitters of this area would be of digital type, as is increasingly common in radio-telecommunication networks. We believe that careful studies of electromagnetic noise in a broad range of frequencies should precede lengthy discussions of the statistical significance of recorded signals. ¿ 1998 American Geophysical Union