There were of course many widely recognised symbols that existed long before the advent of heraldry and it should be no surprise that some of these were adopted as charge in coats of arms A Complete Guide to Heraldry, A.C. Fox-Davies, Bonanza (re-print of 1909 Edition), New York, 1978, P301. The caduceus is a typical example, adopted into the catalogue of heraldry and bringing with it its traditional meaning as the rod of Mercury, it usually is only to be found in the crest and not on the shield. A Glossary of Terms used in British Heraldry, J.H. Parker, Oxford, 1894, Entry:Caduceus