I'm always afraid that if I honk at someone not paying attention they are going to think it means to go and thus cause an accident with the package car or with another driver...you can't just start honking for every little thing the general public aren't going to understand what is expected of them.
Over here, one way management will tag you with an accident is for not using the horn at every possible point of contact...parking lots, driveways...anything. Our standard is " the accident is preventable unless the driver did
everything possible to prevent the accident, up to and including
anticipating the hazard". In other words, unless someone rear-ends you, it's preventable, and if you didn't honk the horn as Grandma plows through that 4-way with her 1966 Buick Electra, it's on you.
Sounds like UPS is taking a page from the FedEx playbook, which is to blame the employee whenever possible for accidents and injuries, even when they probably were not preventable. Using this sort of logic, if a piece of space junk falls-off a satellite and hits your truck, it's your fault because you didn't anticipate the hazard and/or tap your horn. Welcome to Package Hell.