You don't have to actively seek people out our walk around wearing a sandwich board, but you can tactfully warn people without giving too many specifics or sometimes even naming anyone.
Many of us have been "sold" on a job only to find out it was not what they said.
Be respectful, factual and not personal if you are asked. If they choose to take the job, then they now know what they are getting into. We all need to help each other out a little more. Good luck.