Dating your martin guitar
rights to the Sigma brand name and trademark had been allowed to lapse by C. Louis Music of Missouri, AMI is not allowed to use the brand name "Sigma" in the U. The model and serial numbers were usually stamped on in ink, but some are known to have been hand-penned. These will have a 4, 5 or 8 digit (7*0XXXXX) serial number stamped or hand written on them. The 'Purple' label (c1972 onward): These are again white labels that had gold & black lettering but this time with a border, often pinkish-brown or violet in color. Pearl "SIGMA" block inlay between 19th and 20th fret. They have a paper label stating "Inspected and Guaranteed by Levin" and "Sigma Guitars" "est 1970" is inlaid on the headstock in abalone.
The DR-28, has a solid top with laminate side and back, and the SDR-28 having a solid Spruce top with solid Rosewood sides and back. Pearl/pearloid inlay position markers on fingerboard. Chrome closed back tuners (11:1 ratio.) The first year is known to have a zero fret. Truss rod adjustment location is on peg head at nut until 1980. 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. Models such as the 52SDR-9, 52SDR-11, 52SDR-14 and 52SDR-15 DO have solid spruce tops and are considered the predecessors to the "Second Generation" models: Most Sigma guitars under the numerical model number 8 are wholly laminate bodies (exception is the DM-1ST.) The top wood is another matter entirely. Models designated "Second Generation" or in the "Marquis" series models had solid spruce tops and the cost reflected this upgrade as well, around 0 in USD more. 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. These guitars are thoroughly inspected and prepared by Martin craftsmen at our factory and carry a limited lifetime warranty.