Claims by the VAN group [Varotsos, P., Alexopoulos, K., 1984. Physical properties of the variations of the electric field of the earth preceding earthquakes, I. Tectonophysics 110, 73–98, and later works] to have developed a short-term earthquake prediction technique in Greece continue to arouse contentious debates [Claims of success in using geoelectrical precursors to predict earthquakes are criticized and defended, 1998. Letters, Phys. Today 51 (6), 15–100; Great debates in seismology: the VAN method of earthquake prediction, 1998. Eos 79, 573–580]. This is partly because of the unknown origin of the so-called `seismic electric signals' (SES) precursors. Their particular characteristics are not those of the usual electromagnetic noise (cultural noise) or of the natural electromagnetic field (magnetotelluric field). In this paper, we show that transient electric signals looking like SES can be generated by digital transmitters of the radio-telecommunication network. Such signals have been observed in different regions of the world, including Greece and Vietnam. Their characteristics have been analyzed in a broad band of frequencies (10 −3–10 3 Hz) in the Ioannina, Greece, site which is considered as the most `sensitive area' of the VAN network. It is concluded that some of the signals recorded at this site and identified as SES are probably of artificial origin, and that the criteria used by the VAN group are not sufficient to guarantee that the so-called SES are not man-made. Without an extended and thorough study of the ambient electromagnetic noise in a broad band of frequencies and better information about the electrical properties of the deep structure beneath the monitoring station, earthquake predictions issued on the basis of signals recorded by the VAN network are of dubious significance.