Recently I learnt how to display messages on content list and content editor pages in admin, which has enabled me to put key info I kept getting asked bang in front of users (mainly what the screen is for and how to get more help).

Use one of these actions:

Content list: views_edit-{post type name}

Content editor: edit_form_after_title

The latter passes $post to your function (i.e. use myfunction($post)) , so grab that and use $post->post_type to check you’re on the right page before showing your message.