>Но старые посохи со змеями были вообще лишены каких-либо крестов

Да. Вот еще подборка фото: http://www.paradoxplace.com/Church_Stuff/Croziers.htm

Хотя этимологию crozier выводят якобы из "креста":
crozier - late 13c., from O.Fr. crocier, from M.L. crociarius "bearer of a cross," from crocia "cross;" also from O.Fr. croisier "one who bears or has to do with a cross" (see cross). The two words merged in Middle English. Technically, "the bearer of a bishop's pastoral staff;" erroneously applied to the staff itself since 1733. http://www.etymonline.com/index.php?term=crozier

хотя м.б. от клюка-крюк-ключ

In Western Christianity, the crozier is shaped like a shepherd's crook. A bishop/head of church bears this staff as "shepherd of the flock of God", http://en.wikipedia.org/wiki/Crosier

http://en.wiktionary.org/wiki/crosse#French 1.stick 2.crosier 3.(France, sports) hockey stick, lacrosse stick, or golf club 4.lacrosse