Nice examples here:
http://www.hobbithouseinc.com/person...fiddleback.htm
But it seems the botanical cause of the grain pattern is a bit of a mystery. For example:
"Modern botany and science still cannot adequately account for what exactly causes the visually-stunning figuring in Fiddleback Maple"
and
"Fiddleback figuring is not to be confused with "compression grain" or "stress grain" found where roots merge into the bole and also on the underside of large limbs"
(see http://www.spectrumhardwoods.com/products/). I suppose your aim would be to examine a tree to detect the presence of fiddleback before felling. Maybe a timber miller could help.