First, let me say I've learned more from about my Sigma from this thread than from any other internet source. Special thanks to S. Webb for sharing his knowlege.
Now, to add to his knowlege...
I have a Sigma DR-11 that I bought in August 1979 (I still have the receipt) for $388.00. It has the newer "est 1970" logo on the head, but inside it has stamped directly on one of the braces "made in Japan for CF Martin & co" and next to it..."DR-11". It has a solid top and apparently laminated back and sides. It also has the abalone inlay around the front binding and around the sound hole and abalone fret markers The curious thing (to me) is that the back appears to 3 pieces. Instead of 1 purfling stripe down the middle, there are 2...eminating from the neck and ending at the bottom about 10" apart. You can see the braces inside following the same lines. I don't know if this is common, but my guitar is the only one I've seen like this.
It's been my only guitar since Aug, 79 (I traded my Madeira A-12 in for it) and It still plays beautifully. I still get compliments on it's looks and sound. I had it professionally set up and re-fretted and a bone nut and saddle installed in 1987 and it's been perfect ever since. kaufman@jdkaufman.com