I too think it is good sign for the reasons you describe. However at least with cave diving the hazards only present themselves after someone has undergone trai

I too think it is good sign for the reasons you describe. However at least with cave diving the hazards only present themselves after someone has undergone training and gained experience which would make abundantly clear what type of hazards exist. I think one of the worst types of hazards and one of the hardest to signpost is presented by low head dams. Signs are absolutely needed to make it abundantly clear it is not a half baked risk of serious injury or possible death. It's certain death. Signs need to describe and illustrate why it's a certain death because people coming across the hazard will typically have no idea what hazard lies in front of them. Signs need to describe why you can't save someone trapped in a recirculating current or you too will have a certain death. Use of generic signs would likely be downplayed because there there is a saturation of other swift water related (don't swim here/strong undercurrent/risk of flash flooding/etc) signs all over the place that mean people may be complacent. For occupational hazards, I would suspect that crush hazards and asphyxiation hazards (confined spaces such as tanks and silos etc) are amongst the worst types of hazards. They're typically very hard hazards to control for (can't just screen/shield the hazard away from operators), it's easy for even well trained people to make mistakes, and hazards can frequently be hard to determine by operators.