That the substance, container or area involves materials that're toxic if ingested, inhaled or absorbed through the skin. The word "poison" communicates a type of hazard one where the mechanism of harm is the substance entering the body not just contact with it.

Pesticides and herbicides, industrial solvents and cleaning agents, heavy metal compounds, cyanide and its compounds, laboratory reagents, concentrated chemical additives and any substance with a GHS skull and crossbones pictogram (GHS06) indicating acute toxicity.

On storage cabinets and areas holding substances, on individual containers where the poison label is not already clearly visible from a distance, at the entrance to areas where toxic chemicals are mixed or used, on process equipment handling toxic materials, and in any space where ingestion or inhalation is a credible risk if proper precautions are not followed.

OSHA 29 CFR 1910.1200 under the Hazard Communication Standard requires that toxic chemical hazards be clearly communicated to workers through labeling SDS availability and training. OSHA 29 CFR 1910.145 covers accident-prevention signs and tags. For toxic substances individual OSHA standards under 29 CFR 1910 Subpart Z apply, such as 29 CFR 1910.1027 for cadmium or 29 CFR 1910.1025 for lead.

Yes, for container labels and SDS sheets that information is required. For area-level warning signs it is not standard to include first aid detail but noting the emergency number or pointing workers to the nearest SDS station is a useful addition where space allows.

Yes. Storage areas for pesticides, rodenticides, herbicides and fungicides are among the common applications for poison warning signs outside of industrial settings. The signage communicates the hazard to anyone entering the storage space whether or not they are familiar, with the products kept there.