To Dave E

If you look at the edge or the sound hole you can check to see if the grain goes through the thickness of the top. Follow a few different grain lines to verify. If its laminate you wiil be able to see the core material.
As far as I know Sigma did not try to hide the fact that they used laminates by "rolling" the veneer over to hide a core. You can use a mirror to check the underside of the top to see if the grain pattern matches.
Just so you know I own an early (sideways "M") Jap DR-7 all laminate that has fooled many seasoned players. I could also be argued that a laminate will stay flat longer given it's "stable" construction as it it not subject to the natural stresses of a drying solid piece.

Hope this helps