If you think about it, every guitar with exposed wood grain will be unique as a fingerprint. Even two tops made from sequential slices from the same log will have slight differences - not obvious to the human eye perhaps but obvious to computer analysis. Put the top, neck, sides, and back grains all together, and you have something completely unique.
If you have high-res photos of a stolen guitar, it may one day be possible to hand them over to a stolen guitar search service that will relentlessly keep comparing images from Craigslist, Reverb, GBase, EBay, used guitar dealers, guitar enthusiast sites, Youtube, etc.
