one of the three Sigmas i have is an original low number(5435) DR-7
that was made in japan and has the paper label inside with rubber stamps on the label denoting model,serial number and Made in Japan.
the label itself reads:

    IMPORTED AND INSPECTED BY
    THE CF MARTIN ORGANISATION
    NAZARETH,PENNSYLVANIA USA
Model
DR7   SERIAL NO. 5435 MADE IN JAPAN

It also has the greek symbol SIGMA and gold lettered SIGMA on the headstock.

I read that Martin took the M from their name and turned it sideways to perfectly create the SIGMA brand.
As SIGMA guitars returned from Japan to the USA they came through the Martin factory in Nazareth,PA to regulate action,intonation,finish,machinehead adjustment and saddle adjustment.


i can only guess i have an early 70's model. It plays absolutely beautifuly with some 30 odd years of age to what at the time was very good quality tonewood from Japan. It has crisp clean high notes and very good mid and low end tones with an overall balance that few other acoustic guitars that i have played can match. The action is low and the neck and fretboard are a joy with ease to play. I will admit to being biased as i own three Sigmas and love them all.