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. While they discontinued this line in 2007
they still have a website. Mine is a DM-1B shown here.
Martin has since let go of the Sigma brand and it was acquired by AMI in Germany, so the old website listing this model is no more. There is some information here.
Still my go to guitar. Love the sound and still love playing it. I do wish I had a smaller body guitar though for times when I don't need all the sound that this one projects. (NOTE: since then I have acquired 2 smaller guitars, the Teton and the Larrivee.)