Serial number 12915 was stamped during October/November 1917 and was shipped to William Lewis & Son in Chicago on December 26, 1917.
Although the tuners are reported as newer, they do appear to be period-correct Dinsmore & Jager #26 machines.
The ebony pyramid bridge is a replacement.
Style 28 features:
Back and sides: Brazilian rosewood
Top: Red spruce (Adirondack)
Binding: White celluloid
Backstripe: Zig-zag pattern
Other period features:
Slotted square and diamond Japan pearl inlays
Ebony pyramid bridge (replacement)
Ebony neck reinforcement
1-7/8" neck width at nut
C. F. Martin stamp on back of headstock
No style stamp
Photos courtesy of Elderly Instruments.
At the time of writing (September 6, 2019) this guitar is available at Elderly Instruments.