Martin 1-28P guitars are scarce with only 19 being made. This example is the last 1-28P and the only one made as a 1-28PS (S=Special).
This special guitar was ordered on May 7, 1930 by Humphreys Music Co. of Long Beach CA. It was stamped on May 10, 1930 and cleared final inspection on May 27 (only 17 days later!)
What was the special feature? It originally had a 5 string neck! It wasn't a 5-string like a banjo but had a fifth banjo peg mounted in the headstock. The guitar is now set up as a 4-string plectrum. The back of the head stock shows where the fifth banjo tuner was fitted but the front of the peghead doesn't show a hole so it must have been re-veneered at some point.
This guitar was made only a month after the introduction of belly bridge on OM guitars. The belly bridge appears to be original and has the correct shallow saddle angle.
The tuners are Grover #90 banjo pegs.
Style 28 features:
Back and sides: Brazilian rosewood
Top: Red spruce (Adirondack)
Backstripe: Zig-zag pattern
Other period features:
Ebony belly bridge
Slotted square and diamond fingerboard inlays
Ebony neck reinforcement
15-fret neck (20 frets in total)
Scale length: 25-13/16"
Tortoiseshell celluloid pick guard
C. F. Martin stamp on back of headstock
No style stamp
Photos courtesy of Jake Wildwood (https://jakewildwood.blogspot.com/2019/08/1930-martin-1-28p-plectrum-guitar.html)