I just bought a Sigma DR-7 with serial# 6465, located in Amsterdam (Holland). First I thought it was ragged (bad photographs), but when I had it in my hands it was actually in great shape. Headstock has the SIGMA in gold capitals with the sideways M (or greek sigma) in "golden mother of pearl" above it. Inside is a paper label saying:
                                             SIGMA
                               C F MARTIN & COMPANY
                                        MODEL DR-7
                                     SERIAL NO. 6465
                              MANUFACTURED IN JAPAN
Bridge saddle is not adjustible. Topnut, saddle, endpins and strap-pin are very cheap plastic (will change). I am pretty sure that top, sides and back are laminated: looking at the side of the soundhole rim shows the venation (lines in the wood) are only in the top mm of the wood and then another colour wood starts. The lines on the sides and back are not near the same on the inside and outside. Nevertheless a beautiful guitar with great sound, now I know what people mean with a grand piano sound from a guitar. I installed new tuners and a bone saddle, new strings and set it up right, and it really sings, the lower strings vibrate like a baritone in a cathedral. As far as I remember, my father's old Martin D-18 sounded a bit more sofisticated, but this Signa seems to have more power (could also be strings or set-up off course). I payed 170 euros ($250) to a friendly beginner, who thought the sound too soft (??), he knew what it's worth, and had other bidders, for the same price. So this is what you pay for a 70's Sigma in Holland (although I have seen people ask 450 euros ($650) for a post 1984 DM-2, probably still on sale). I am very happy with this beauty, it's just the price/quality combi that's right for me. And I love early 70's gear...