I do know some Civil War surgeons wore the letters "M.S." (Medical Staff) on their shoulder straps. That would be a real neat find if it dates from the Civil War!
The symbol is a medical cadusa (I'm sure I spelled that wrong sorry). It is a symbol of all medical Drs. , the MS I don't know but that is a great find I doubt many of us would see one in our life time, thats what makes this fun all the odd finds that we get to see.
Mchamby