I was a little confused by the Caduceus reference because in the US it is used to denote doctors, not pharmacists (we use the mortor and pestle as the symbol for pharmacists).
I did a little Wiki work and found out that Caduceus is used by other countries for the symbol of pharmacy(from http://www.rpsgb.org/pdfs/mussheet13.pdf): "The symbol of two snakes on a staff is called the Caduceus. The staff,
depicted with wings, is that of Mercury (Roman) or Hermes (Greek), messenger of the Gods and also God of commerce. (The Greek root of the word Caduceus means “herald’s wand”). The history and meaning of this symbol is complicated. In the West it has been adopted as a symbol of
medicine since the 19th century, probably because of its similarity to the serpent of Epidaurus on the staff of Aesculapius. It is generally considered less suitable for pharmacy than the one snake motif (the bowl of hygeia), but is more popular for use as a general medical symbol."
It's just a little rough. Something this simple needs a bit of something to make it pop. Cleaner lines, or highlight/shading, or ...something. Some polishing.
a little detail and you're in business. Make it look like an actual medical shirt and then, 5 seconds after the person has turned away, have them be like "oh damn, that was a friggin guitar in that!"