I goofed. Rich (Sheepherder) pointed out to me that my illustrations and text were somewhat in error. I was correct that the "N" stamp on the gun was the result of rotating the stamp 180 degrees so that the resultant stamp is upside down, therefore the left example is a correct representation of an inverted stamp, but not a mirror image (scratch out "mirror image" in the text and example image
).
Here is what a mirror image would look like (and it isn't what is on the gun).
Ron