Don,
The "Fish" symbol is based on overlapping two circles creating what's known in the Sacred Geometry as the Vesica Piscis or Mandorla. The early Christian Church simply extended the lines of the circles creating a fish looking symbol, and it was supposed to be a secret symbol used by early Christians to identify each other....or so I've read!
Within the Vesica Piscis, using a straight edge, a series of triangles, squares and mathmatical functions are created, and from these King Solomon's Temple was built. Also, the pyramids of Egypt, Mesoamerica and other places as well as all of the catherals of the Middle Ages in Europe were designed using the Vesica Piscis. Also the National Catheral in Wash.DC. The tombstones of both Daniel Boone and his father, Squire, are inscribed with the first steps of making a VS, and it is from this as well as other records that we know both were Freemasons.
We have two original Gillespie Rifles found in my home county of North Georgia made from Hanging Dog Iron which have Hex marks around the muzzle. Very common with Southern Mountain Rifles. Someone knowledgable of Masonic symbols will also see these on occasions on old original rifles. The "Free Born" rifle on Mel Hankla's website, as well as Mel's "Folky Artist" powderhorns are good examples of this!
Rich P.