I'm not sure why the arrow was pointing down, but this is an idea I had. (Karen, correct me if I'm wrong.) I know during the convention in the 30's Pi Phi decided to replace I.C. Scorosis with the letters on the badge. Maybe around this same time they decided the uniform way to wear the badge? If you have ever seen old pictures you'll see members wearing the arrow everywhere...in their hair, on their collar, on the right side of the blouse.
Personally, I would feel weird wearing a pin in my hair.