Serial number 48106 was stamped on August 26, 1931 and cleared final inspection on December 1 that year.
This guitar was made shortly after the change from banjo tuners to side tuners and the larger pick guard were made.
The tuners are replacements but the original tuners would have been Grover G-98 clipped plate machines.
Unusually, this guitar has a C. F. Martin decal on the front of the headstock. The deal didn't come into use on Martin guitars until 1932 so its presence indicates the guitar was returned to Martin for some repair work at some point.
Style 18 features:
Back and sides: Mahogany
Top: Red spruce (Adirondack)
Binding: Black celluloid
Other period features:
Ebony belly bridge
Ebony neck reinforcement
1-3/4" neck width at nut
Tortoiseshell celluloid pick guard
Dot fingerboard inlays
Decal on front of headstock
C. F. Martin stamp on back of headstock
At the time of writing (May 27, 2019) this guitar is available at Steve Swan Guitars (http://www.steveswanguitars.com/items/vintage-martin-other-size/1931-martin-om-18/)
Photos courtesy of Steve Swan Guitars