I got the Sigma in 1988. Its a Japanese Martin. I probably play this one the most. Its got a rich, full bodied sound, and it plays nice. Sigma guitars were based on standard Martin models and were inspected at the Martin factory before going to market. I had initially thought the model was DM-1B, but now believe in is DM-18. The DM stands for "Dreadnaught Model". Update 4/2021 it's actually a DM-19
The top is solid spruce, stained brown. The sides and back are laminate mahogany.
Between 1988 and 2020 this was my only playable acoustic and I played it all the time. It has a bold sound as you would expect from a dreadnaught and very playable action. In 2020 I expanded my collection significantly with smaller guitars better suited for playing solo, but the Sigma still stands out with the biggest and brightest sound.