These two symbols have very different meanings! If you want to refer to medicine, use the rod with one snake, the Rod of Asclepius! If you want to refer to commerce (or some other things, see below) use the winged staff with two snakes!
The Rod of Asclepius is the symbol on the right. It is a rod with one snake wrapped around it. It is the symbol for the ancient Greek god Asclepius, known as a god of medicine. It is used today as a symbol for the medical profession. You can find the symbol on ambulances in the US and all over the world, and… everywhere.
The Caduceus is the symbol on the left, it is a staff with wings and two snakes wrapped around it. It is the symbol for the ancient Greek god Hermes. Hermes is known for being a messenger of the gods, guide to the dead and protector of merchants, shepherds, gamblers, liars, and thieves. The Caduceus is generally used today as a symbol of commerce.
Why do they get it wrong in the U.S.?
In 1902 the US Army Medical Corp chose the Caduceus as their insignia. Most scholars regard this as a flat-out mistake. The US Army writes that the Caduceus represents “the non-combatant status of military medicine on the battlefield”. The Encyclopedia Britannica notes, “Among the ancient Greeks and Romans [the Caduceus] became the badge of heralds and ambassadors, signifying their inviolability.” So maybe the US Army was thinking the symbol would convey a sense of “… Hey, hey, hey, don’t kill me, I’m just a messenger delivering the wounded to the hospital.” or some such. That feels like quite a stretch to me. The army probably just chose the wrong symbol. More importantly, saying “I’m just a messenger” is, at best, nonsensical on a doctor’s clothing. At worst, it’s terrifying! A person wearing this badge would be, in theory much more likely to kill you (guide to the dead!), sell your organs (protector of merchants!), feed your body to the dogs (shepherds!), hock your jewelry (gamblers!), and tell your mom they haven’t seen you in a week (liars and thieves!) than help you. Seriously!
There are many articles where historians and professionals delve into this issue. Almost all of them say the US Medical Corps are definitely using the wrong symbol. Here’s a few to get you started:
- Finn, R., Orlans,D. A., Davenport, G. (1999). A much misunderstood caduceus and the case for an aesculapion. The Lancet, 353 (9168), 1978. http://dx.doi.org/10.1016/S0140-6736(05)77199-3
- Wilcox, R. A., & Whitham, E. M. (2003). The Symbol of Modern Medicine: Why One Snake Is More Than Two. Annals Of Internal Medicine, 138(8), 673. http://www.ncbi.nlm.nih.gov/pubmed/12693891
- Things you don’t learn in medical school: Caduceus http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4439707/
- Wikipedia has a trove of well referenced info about the subject: Caduceus as a symbol of medicine, Caduceus, Rod of Asclepius, pictures of Ambulances,