Still adamant on using that poster idea? Well consider these innovative takes on the usual street poster.
1. This anti-abuse ad from Spanish organization Aid to Children and Adolescents at Risk Foundation (ANAR) has a hidden message only audiences below a certain height can see (i.e. possibly abused children with none-the-wiser adults)
2. This street poster (from 2009) changes the image only when noone is literally looking.