The real Voodoo will have a 4 character code on it, along the lines of SVS7. This means Stiff, based on the VS shaft, and 70 gram range. There is a RVS7, and a model based on the NV, so SNV7 etc, too.
The Made for Titleist/Callaway etc will say that.
The important difference is that the real one plays stiffer, as much as 1 flex difference according to some clubfitters.