A number of early instruments have a "C. F. Martin/New York" stamp impressed in the back of the guitar near the heel of the neck. This stamp was sometimes applied lightly and can be hard to see, especially on darker wood.
Many of the Martin guitars with either ladder bracing or 3-strut fan bracing (i. e. to about 1841) have this stamp. For some reason none of the guitars examined with 5-strut fan bracing or early type of X-bracing bear the Martin stamp in this position. So, most of the guitars between 1842 to 1850 do not have the Martin stamp on the back.
The Martin stamp resurfaced about 1850 but mostly disappeared by the end of the decade excepting on guitars with black necks. For the most part the Martin stamp only appeared on the lower priced 3-17 and 2-1/2-17 guitars. This practice continued until the 1890's.
1834 Martin Guitar