Why do we need OSHA signs?

Is it an absolute requirement in the workplace?

OSHA 191.145(a)(1) use of signs or symbols that indicate and, insofar as possible, define specific hazards that could harm workers or the public, or both, or to property damage. These specifications are intended to cover all safety signs except those designed for streets, highways, and railroads

https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.145

https://www.smartsign.com/fod/ss/safety-signs