A sign with the signals in Dutch. It says: Electric signals above ground, extraction personnel, three strokes: up, four strokes: down, if the electric signals are malfunctioning use the manual signals: 1 stroke: stop, 2 strokes: hue, 3 strokes: down, 4 strokes: up. This bothers me, so in case of an emergency (the signals don't work) there are other signals used to go up or down.