I'm getting a little annoyed here because I am often asked to design society logo's for .... societies; usually medical ones.
If you notice on the back of an ambulance, you will see the typical symbol of the staff and ONE serpent wrapped around it, this is the Greek symbol for medicine (Asclepius).
However, if you just do a quick search for Medicine Logo, you will find that most of their logos actually represent the Greek symbol for commerce (Caduceus).
According to Wikipedia, this is a mistake made common by North Americans.
**** you United States. I am one-by-one fixing Singapore's medical society logos.