The power cable sign

You would think that the sign is telling us that a power cable is crossing the canal, but there are none to be seen. Maybe its a warning to submariners and totally lost WW2 German U Boats, that there are cables lurking in the murky depths of the Caledonian Canal! I always jump when I'm level with the sign. Just in case.

PS The one darting across the picture is not a power cable, but a mere telegraph wire.