We tried the more positive and proactive approach here too.
I have NEVER told Charlotte "Don't talk to strangers", I hate that she should feel unsafe simply at the sight of someone, and I don't agree with it. She speaks to strangers all the time - the old lady in the supermarket, the postman when he comes to the door, the older child and his father in the park... There are occurances everyday where it IS ok to speak to strangers, so I am not comfortable with the fear blanket approach.

Charlotte knows that there are no secrets from mum and dad. Ever. That nobody should ask her to keep anything secret from mum and dad and if they do then she knows it is wrong. She knows not to talk food from strangers, that she should never go anywhere with anyone, without telling mum or dad first.
We teach her her address, our Christian names, she can identify herself if she is lost and she knows to speak to another mummy with children with her if she is lost or in trouble and can't find mum or dad.
Charlotte knows that nobody else is allowed to touch her body and she knows that if anyone tries to touch her she is to scream as load as she can and run away.

Charlotte knows there are bad people who do bad things, but I refuse to let her live in a bubble of anxiety and fear of anyone unknown.