The rift, or Vs, should be on the top and/or bottom of the arrow. Or, stated another way, the grain should be perpendicular to the side of the bow. On really good shafts with straight grain, there may not be rift on both sides of the arrow. I always use the straighest end of the shaft as the nock end.
I wouldn't be too worried about the direction the rift is pointing. I've been making wood arrows for 40 years and have never had one break at release. I've broken a lot of arrows, but never that way. I only use very straight grain shafts though, and always place the straightest grain on the nock end.
However, I've seen a lot of junk wood where the grain is running off the shaft. These should really be culled, but if one does use them for stumpers or whatever, it wouldn't hurt to follow TJ's advice, in which case you would want the rift on the bottom pointing toward the nock end. If a shaft gives you that on either end, use the straightest end for the nock end.
The important thing is to have the grain perpendicular to the bow site window, its strongest orientation. Placing the rift perpendicular to the bow site window is what's dangerous. A lot of folks, even folks who sell their wares, make this mistake.