I found some comments from Sheldon Brown that were precisely what Don has said, that the V should point toward the direction you are going.
But, Sheldon made the point that tread patterns have very little function since the tread is not very deep.
Back to the Motorcycle, the tread direction is opposite if this. His is a more open V but the rotation arrow clearly points one way:
Looking down at the tire:
Front of Bike
\ / ^ + Rotation Arrow \ / | \ / | \ / |
What about the double V pattern? I would think pointing the V's forward too would be the way to go.
/\||/\ /\||/\ /\||/\ /\||/\
Mike "Motorbike tires confuse me" Wilkinson Castle Rock, CO