What must be remembered is that the Pennsylvania Dutch, Moravians and Quakers were deeply religious people. Some like the Pennsylvania Dutch were more than a little superstitious.
While some theorize that these decorations were just that, decoration, the frequency and amount found prove otherwise. Some of these decorations were even hidden. An examples of this is the INRI and DEO found on the bottom flat just behind the muzzle on some J.P. Beck rifles. In this same area you may find a cross or more commonly an X below the front sight. This is said to ward off a demon who would ride the ball causing an inaccurate rifle.
In case you are wondering, INRI and DEO are both Latin abbreviations. INRI was tacked on the cross by the Romans meaning " Jesus Christ King of the Jews". DEO means, " With the help of God". On Beck rifles some times this is found....... "J Deo Beck".
Concerning the fish. Inlays are more common on post 1800 rifles. As the 19th Century progresses inlays tend to replace carving as a decoration on longrifles. The fish symbol goes way back to the early Christian times when Christians had to meet in secret. Legend says that these meeting places in the catacombs of Rome were marked with a fish or the ichthus. One fish means Christ where three means the Trinity. Conestoga Wagons from the same region had a fish shaped axe holders.
Frontier lore does say that a rifle marked with a fish does shoot better. Also legend says that if a new barrel was inaccurate it was removed from the rifle and unbreached. It was then placed in a stream muzzle facing upstream , the same way a fish faces. It would remain here for a few days to wash the evil spirits out of it.
Think about this for a moment. This may very well have some merit. If there were burrs or areas of the barrel too sharp, a few days in fast moving stream where silt and corrosion worked on these areas. That and the vigorous cleaning the bore got after the barrel was removed from the stream, I'm sure it would shoot better. This could be just another method to lap the bore.
Here are some more Christian symbols..
Eight pointed or Hunters Star... Star of Bethlehem
Distlefink or thistle finch a small bird that makes it's nest in thistle... the thorny crown of Christ
Bleeding heart... the fifth wound of Christ
Acorn... strength, character, Christ or Mary
Serpent ... warning against the Devil or the healing serpent of Moses. If it is a rattle snake it takes a totally different meaning... Don't tread on me.
Daisy, Tradition calls it a Daisy but it bears a closer resemblance to the wild rose... Innocence
from 1970 edition Gun Digest