Hi,
Inlays of bone, metal, shell, and wood go back at least as far as crossbows. Metal inlays on rifle cheek pieces certainly pre-date the American Rev War. Interestingly, of the 45 guns shown in "Steinschloss Jaegerbuchsen" only 8 or 9 have inlays on the cheek pieces and almost all are bone, wood, and ivory. A couple have metal inlays there. The practice of putting a star of some sort on the cheekpiece seems to have become somewhat popular after 1750.
dave