Rifle #45, in William W. Ivey's book, "North Carolina Schools of Longrifles 1765 - 1865" features an "iron trigger guard held on with two wrought nails rather than pins or screws." This rifle is from the Early Deep River School and was likely made in Randolph County.
Rifle #194, in the same book also "has an iron trigger guard held on with hand-made wrought iron nails." This rifle is from the Catawba Valley School and was found in Catawba County. This rifle has no butt plate, but does have an iron nail at the juncture of butt and comb.
These are the two examples that I know of that have trigger guards held on with nails. They are not common, but do exist.
Michael