These marks are on the outside of the 16 gauge barrel. THe right barrel is a 9.3x72. There are no pictures of the flats or water table. There is a mark in front of the charge and load stampsand is a Crown over something. Unfortunately it is not clear in the picture. It would appear to be a G much more likely than an S. I am going to contact the seller and see if he will check it and also send pictures of the barel flats and water table.