Greetings! I've a Sigma GCS-6 that I purchased new in 1974 after sampling similarly priced Yamahas, etc., and the Sigma outshone them all. This info should be pretty accurate for dating GCS-6 Sigmas made from '70-78. The early models were solid wood, in this case a spruce top, mahogany sides and back, rosewood bridge. The original peghead logo for Sigma is in gold with Greek symbol Σ above in mother-of-pearl. There is a paper label with a silver gray border which has SIGMA with CF Martin & Company underneath. Then there's the model, serial number and "Manufactured in Japan". On the back of the peghead there's a label that reads "Made in Japan." I never learned to play her but now I think I will.