Around campus here, there are CCTVs everywhere. You can see them, even if you didn’t look too hard… Still, there are signs close to every placement saying, “You are on CCTV”.
Barring other reasons, I have come to see a wisdom in it: even when people around you could see something, you have a responsibility to tell them. Make them see. Show them. Direct their attention to it…
It’s not enough to say, “…but it was obvious.” or “…you should know.”
Maybe they indeed should but help them. Help yourself. Ignorance is never enough an excuse, but you can help them to avoid that excuse altogether.