Jenst

Add a short note about the latest changes in the current post or page.
WP Update message adds a metabox in admin post or page section. If you updated a post or page with important information you can write a note about it here.
There are a few optional settings, but the plugin works fine even without changing anything.
<h4>Settings</h4>
You can choose a style theme and more.
<ul>
<li>Published date format (if published date should be included)</li>
<li>Updated date format (if updated date should be included)</li>
<li>Position</li>
<li>HTML</li>
<li>New row replacement</li>
<li>Style theme</li>
</ul>

WP Update Message

Add a short note about the latest changes in the current post or page.

Valice

Banner alerts are custom alerts to notify your website visitors of promotions, alerts, events, etc. These display at the top of the website until they are dismissed by the visitor. Any new visitor who has not been to the website will see these until they are dismissed.
Banner alerts are configured just like a post or page with support for title, content, and excerpt. The plugin settings allow you to define which parts of the alert to display and whether or not to link to the full post. You can run more than one alert at a time and activate or deactivate as needed.
This plugin is ideal for:
<ul>
<li>Important operational changes</li>
<li>Technical notices</li>
<li>Time-sensitive appeals for donation or action</li>
<li>Terms or agreement changes</li>
<li>Privacy notice acknowledgements</li>
<li>Service outages or maintenance messages</li>
<li>Special offers or promotions</li>
</ul>

Banner Alerts

Provides an easy interface for creating and displaying alerts or notices as a banner on a website

WP Update Message vs Banner Alerts