I know this post is primarily concerning the recreation of the logo for costumes, but it still seemed the most appropriate place to insert this comment.

Apparently the caduceus symbol is not actually medical in origin, it is just frequently confused with the medical Rod of Asclepius, which looks similar (a single snake and no wings). The caduceus is associated with Hermes (or Roman Mercury) and has connotations of theft, commerce, deception and death, among others. 

I'm wondering if Joss & Co. knew this or not, as the irony would be pretty fantastic. I'm lifting this quote directly from the caduceus Wikipedia article (my own underlining): 

As god of the high-road and the market-place Hermes was perhaps above all else the patron of commerce and the fat purse: as a corollary, he was the special protector of the traveling salesman. As spokesman for the gods, he not only brought peace on earth (occasionally even the peace of death), but his silver-tongued eloquence could always make the worse appear the better cause. From this latter point of view, would not his symbol be suitable for certain Congressmen, all medical quacks, book agents and purveyors of vacuum cleaners, rather than for the straight-thinking, straight-speaking therapist? As conductor of the dead to their subterranean abode, his emblem would seem more appropriate on a hearse than on a physician's car.