There are currently mintage lines, with and without SM. All the copper Mainz (and Erfurt) coins of that era (1756-1761) have SM on the reverse. None of the images in KM, Schön DM, and Gräßler (several hundred images in Gräßler) are missing SM, and I can't find any images on the web without SM.
The owners of the SM mintage line should be moved to the other line and the SM mintage line should be removed.'
Edited: The 1761 line doesn't belong on this type. Where should it go?