I bought a new Korean built Sigma 000-18 in the early '90s (serial number starts 9308, the rest is obscured by the 000-18 stamp but might end 0092). Although cosmetically it is not perfect (the body end of the fretboard is badly finished) I've had no complaints about it's sound. I bought it from a shop owned by a local Luthier who was extolling the virtues of these guitars for their price.
From what I've read these guitars have a solid Spruce top (mine definitely has)& laminated mahogany back & sides. Mine (chosen from 2 in the shop at the time)has a flamed maghogany neck and a fine chevron flamed mahogany back (split from the centre seam outwards). This is not some photo-flame effect which they apply to cheap electrics, as the flame moves as you tilt the guitar. The flame is visible on the inside (back) of the body as well, although not matching the direction of the pattern on the outside. What I don't understand is why they would use flamed mahogany on the inside of a comparatibely inexpensive guitar !

For information (for those interested in current prices) - there is a Sigma DR41 for sale in a local guitar shop for £299.00