These signs are known as
Jupiter's staff in Roman mythology. Jupiter was the Roman equivalent of
the Greek god Zeus and the Germanic god Woden or Odin. See , Odin's staff, in Group 24.
The sign for the fish spear, or , is the staff of Poseidon (Greece) or of Neptune (Rome). Jupiter's staff is this staff doubled. If we remove the barbs from Jupiter's staff and turn it 90 degrees we are left with the graph for the zodiacal sign of Pisces. It is not surprising, then, that both Jupiter (according to the old tradition) and Neptune (according to modern astrology) are the ruling planets of Pisces.
The ideogram is quite common on rock carvings from the neolithic age.
Compare the staff of Jupiter with the sign for the staff of the Assyric-Babylonian godhead Adad, . Whatever variation, all these staffs of the mightiest of the gods were associated with lightning, thunderstorms, and the power to agitate the waters.