[Just another Joe]

Their shape is so you can hang them on a tree.

Actually, their shape is supposed to be the same as a shepherd's staff.

[Verginius Rufus]

If it is in the shape of a shepherd's staff, then maybe it is meant to honor David.

Or it could be a Pi, standing for Pentateuch (the five books of Moses, recognized as scripture by Jews, by Samaritans [all Samaritans, not just the good Samaritans] and by Christians).