Unpublished Warnings is a free WordPress plugin that warns you and your blog authors when looking to an unpublished blog post that just happen to be able to see.
All you need is install and activate it, it automatically enables a small notice on the top of all unpublished WordPress posts that are pre-viewed outside the visual editor by clicking its “preview” button. This notice works as a small reminder that and reminds you that the post is unpublished and it can be dismissed with a single click.