Jonathan Bardo

<p><strong>Note: This plugin only works with WordPress 4.2 or higher</strong></p>
<p>This plugin will enable the site administrator to easily create an admin message present on all pages. The admin has the option to let the user dismiss the message for the duration of his session.</p>


Admin User Message

This does just what I want. Thanks for making it. :)
It's definitely better than https://wordpress.org/plugins/admin-screen-messages
You might want to also tag it as:
https://wordpress.org/plugins/tags/admin-message



Perfect

Add message to users of your site. Choose wheter they can dismiss it or not.

Tayyab Hassan

<p>Add a custom footer message to your WordPress site. Lightweight and easy to use.</p>
<p>This plugin allows you to easily customize the footer message on your WordPress site without editing theme files.</p>
<h3>Features</h3>
<ul>
<li>Add a custom message to the footer.</li>
<li>Manage footer text easily from the admin settings page.</li>
<li>Lightweight and beginner-friendly.</li>
<li>Fully secure with sanitized inputs and escaped outputs.</li>
</ul>
<h3>License</h3>
<p>This plugin is licensed under the GPLv2 or later. You are free to modify and distribute it under the same license.</p>
<h3>Notes</h3>
<p>Developed with simplicity in mind. Feel free to contribute or suggest improvements!</p>


FooterMate

Add a custom footer message to your WordPress site. Lightweight and easy to use.

Admin User Message vs FooterMate