Here's a good rule of thumb.
Many employers are unaware of illegal harassment until they receive a formal complaint.
One clue harassment may be occurring in your workforce is an employee who clearly avoids a supervisor, another employee, a vendor or a customer. It is important to ask that employee if he or she is experiencing problems if you suspect harassment. Management should also document the conversation and conduct a thorough investigation if harassment is reported. Complete a thorough investigation of the alleged occurrence within 1-2 weeks of any complaint or report. First, interview the target of the harassment and document all details, including who, what, when, where and how the harassment occurred and all potential witnesses.