Dating your martin guitar
Martin completed and finished them alongside the regular Martin production line. Some consider the DR-35N to be a prototype of the inexpensive laminate Martin Shenandoah line of guitars, it appears only 2907 of these Sigma Martin USA guitars were ever produced in total, though there may have been others that did not make final inspection and hence were not serialed (I personally know of one such Sigma-Martin,) and are the only Sigma related serial numbers publicly available from Martin at this time.
Bridges and tuners may have been installed, as well final sanding and finishing before strings were installed and a final set-up was done. Serial numbers for Sigma guitars built in South Korea, Taiwan and Indonesia are perhaps even more meaningless, though again some seem to indicate the year of manufacture (e.g.
No solid top Sigma under numerical model designation "8" exists, save for the DM-1ST (Solid Top.) Further, tests conducted on the 52S models with model numbers below "8" show that they are, in fact, wholly laminate bodies.
In 2011 the German company "AMI Musical Instruments Gmb H" purchased the rights to the name and relaunched Sigma Guitars again, this time being produced in China. This is especially true of unusual, special (sample/prototype models) and/or low production number models (e.g.: DT-30.) The 'Gold' label: The next generation of labels are transition labels that are white w/Sigma and three horizontal lines in gold ink, the Greek sigma in black and printed black text (Made for C. The Σ symbol now also in this same pink/purple color. Later examples have gold plated, Sigma embossed Schaller style enclosed tuners (ratio unknown.)GCS-4 Grand Concert. There is a DR-14 on display in the Sigma Museum in Munich, Germany.Actually this is not correct (read below) Copied from the Sigma Generation III brochure: (see below) High quality is readily apparent in the SDR-28 and SDR-28H rosewood Dreadnought with its rich appearance and wide range of features: solid spruce top, scalloped top bracing, rosewood back, sides, fingerboard and bridge and carved mahogany neck. Adjustable rosewood bridge to approximately 1975, non-adjustable thereafter.