You should always make sure your company's drivers know that you've got dash cams installed. Of course, they'll probably spot them as soon as they get into their vehicle, but you need to make it part of your driver onboarding process to explain that dash cams are in place, and explain why they're there. Other than that, it depends on which state your team drives in. If your state's law requires you get consent from all passengers before recording audio, then those passengers will need to be told there's a dash cam in the vehicle (unless you simply disable the audio recording function).