This guitar is an early Martin 0-27 and is unusual for a number of reasons.
Most collectors are familiar with 2-27 guitars that make up the large majority of style 27 guitars made. Size 0 guitars in style 27 are quite rare: only thirty-nine 0-27 guitars were made between 1856 and 1863 and of these only twelve had friction tuners.
Many collectors are also aware that the style 27 guitars have an abalone sound hole ring. This is the normal feature for smaller body style 27 guitars but, for a brief period between 1856 and 1858, 0-27 guitars had an ivory sound hole ring like a period style 28. It is a little hard to tell for certain but the switch back to the abalone sound hole ring for the 0-27 guitars seems to have taken place in 1858.
Considering the zig-zag back stripe on this guitar, it might be suggested this guitar is actually a 0-28 where style 27 purfling was substituted for the usual herringbone (not unheard of in this period, since Martin considered both patterns as "fine). However, another nearly identical guitar exists from the same period and it has brass tuners, a feature of style 27 instruments. See the entry for the other guitar for more details.
Back and sides: Brazilian rosewood
Top: Red spruce (Adirondack)
Purfling: Style 27
Back stripe: Zig-zag pattern
Ivory friction pegs
Other period features:
Ebony belly bridge
Ebony neck reinforcement
1-7/8" neck width at nut
C. F. Martin stamp on back of headstock
No style stamp
Photos courtesy of Gruhn Guitars