One of the areas of mid-19th century medical practice I have been researching concerns the use of "poison" notices and red labels on vials and bottles. I wanted to share some information.
I seem to recall a brief discussion on this forum to the effect that mid-19th century medicine vials/bottles did not contain any label warnings and that any such warning labels were post-war. On the contrary, my research shows that such warnings were being used prior to the war (see, e.g., Edward Parrish, A Treatise on Pharmacy (1859), p.689, which specifically mentions the prudent practice of writing "poison" or "use with care" on medicine with lethal potential); additionally, the use of red labels to distinguish poisons from non-lethal medicines, which were labeled with white pieces of paper, was reportedly being used by pharmacists in France as a result of a regulation dating around 1856 (see, e.g., Vol. 53, Boston Medical and Surgical Journal (1856), p. 196, citing an article in the Lancet.) See also, Vol. 5 American Journal of Pharmacy, p. 499, which contains the minutes of the Proceedings of the American Pharmaceutical Association's 1857 annual meeting during which an appeal was made to American druggists to mark all vials/bottles containing poison with the word "poison" in "a distinct and unmistakable manner" as well as "some symbol" such as a "bright red piece of paper" or "Greek cross" to give the eye "an additional means of cautioning you when handling" the medicine.
I primarily reenact in the realm of civil medical practice so I am not claiming that practices similar to the above were being used by the US military during the war or that such practices were universally implemented even in civil practice; however, I wanted to provide some actual research supporting the awareness of the prudence of the practice, at least among mid-19th century civil medicine practitioners.