The book "Gunsmiths of Bedford, Fulton, Huntington, & Somerset Counties" by Jim Whisker illustrates in multiple views a fine, signed Samuel Mier rifle on page 118. The barrel signature reads "Sam Mier Somerset ? " with the last two letters unreadable [to me] and perhaps "Co." The capital script "S" in both his name and the county name are very similar to the script S on the side plate, and the last names are almost identical as well.
I think the large print "S" on the double rifle may be a later "correction" for the lost original script first initial. If you blow that picture up, you can see a couple of dings in the barrel iron under the print "S", with the S cut through the dings rather than being damaged by the dings. It suggests the print "S" was cut well after the dings were put in the barrel, and probably added later to replace a missing or damaged first script letter. Shelby Galllien