Chemical, biological (CB) — and sometimes radiological — warfare agents were assigned what is termed a military symbol by the U.S. military until the American chemical and biological weapons programs were terminated (in 1990 and 1969, respectively).
Military symbols applied to the CB agent fill, and not to the entire weapon.
A CB weapon is an integrated device of (1) agent, (2) dissemination means, and (3) delivery system.
For example, chloropicrin has the symbol PS, which was derived from the British town in which it was manufactured during the First World War: Port Sunlight.
[1] Material Testing Program EA (Edgewood Arsenal) numbers: United States Army Chemical School.