You may post posters or flyers of missing children as you have done in the past - according to guidelines - as you have room etc. However, we ask that you post them on a bulletin board not on the front door.
Hope that clarifies things
Links:
[1] https://my.metrolibrary.info/drupal/sites/default/files/admin_files/clarification-posters.pdf
[2] https://my.metrolibrary.info/drupal/tags/displays
[3] https://my.metrolibrary.info/drupal/tags/guidelines