Just remember not to pin through both the outer and inner aprons.
The pin should be through the outer apron only.

And it's first function is just a weight to hold the apron down in a breeze. So lower and closer to the fringe is better than higher and further away.

The second reason for the pin is a bit of bling or flash. So wear what looks good to you. I'm fond of my little silver kokopelli that started out as a ladies necklace.