Z-Dad,
The angle of the spin axis of fastballs is directly related to the arm-angle of the pitcher at his release point.
12-to-6 spin usually characterizes the topspin of an over-the-top curveball while 6-to-12 spin characterizes the backspin of an over-the-top fastball.
However, very few pitchers have a true "over-the-top" arm-angle at release. Guys like Sandy Koufax, Hideo Nomo, Trevor Hoffman, etc have very high arm-angles at release, but even these guys aren't really at 12 o'clock. 11 o'clock for the RHPs and 1 o'clock for the LHPs is more accurate.
So, anyway, for true "over-the-top" fastball release of a striped ball the stripe would appear as vertical on the face of the ball.
A pure 3/4 arm-angle at release would show the stripe on the face of the ball at a 45 degree angle.
A side-armer's release would show the stripe as horizontal. Check out this clip of a side-armer's split-finger fastball, for instance:
http://www.youtube.com/watch?v=VkMSO1BhKVw