These warning diamonds relate to shipping and now also have relevance to storage. The 1 means class 1 (explosives) the 4 is the hazard type, 4 means "Substances and articles that present no significant hazard". The S and G are the compatibility groups.
The definitions are:
G- A substance which is an explosive substance because it is designed to produce an effect by heat, light, sound, gas or smoke or a combination of these as a result of not-detonative self-sustaining exothermic chemical reactions or an article containing such a substance or an article containing both a substance which is explosive because it is capable by chemical reaction in itself of producing gas at such a temperature and pressure and at such a speed as could cause damage to surroundings and an illuminating, incendiary, lachrymatory or smoke-producing substance.
S- Substance or article so packed or designed that any hazardous effects arising from accidental functioning are confined within the package unless the package has been degraded by fire, in which case all blast or projection effects are limited to the extent that they do not significantly hinder or prohibit fire-fighting or other emergency response efforts in the immediate vicinity of the package.
