The policy should be prominently displayed in your employee manual, posted in appropriate places, made known in no uncertain terms to all employees, and consistently enforced. If someone violates the policy, take action. Fire the individual. Employers are too concerned these days about what generally amounts to baseless litigation. Take the time and make the effort to train managers.
Managers are ultimately responsible for the people they supervise.
It is not the HR professional's job to seek out and counsel problem employees. The HR professional s job is to consult with the manager and the intervention team to decide upon the best course of action. Above all, trust your gut. While still somewhat rare, workplace violence has become more prevalent in recent years. Employers need to recognize the potential liability associated with what were perhaps once idle threats but which may, through circumstance, be a precursor to physical violence.