The samplerInfo node has a flag called flippedNormal that returns either a 0 or a 1 depending on which side of a single-sided surface you are seeing.
Many people use this to drive a Maya conditional node and so create something called a double-sided shader - a single surface with one texture on one side and another texture on the other side.
The syntax for the conditional node can be confusing to some Maya users. If you'd like an easier to remember alternative, consider using the flippedNormal flag to drive a blendColors node instead.
Wow, thanks man! so nice and simple, works great. I remember looking at a tutorial a while back on how to make a double sided texture - i dont remember any of the content, just my reaction after reading it, which was "WTF??!" So thanks alot dude!