marco.rucci

This plugin allows you to create strong evidence of intellectual property on the post content by certifying a blog post using the criptographically secure process of trusted timestamping. The timestamps are issued by an accredited Certification Authority, thus adding legal value to the certification. The certification guarantees that the post content is not modified since it has been published.
Coming soon: each certified post will show a “certification seal” that links to a page on easytimestamping.com where verification is performed on the fly. The verification checks that the post content has not been altered and checks that the timestamp associated with the post has been issued by a Certification Authority and verify its authenticity. The “certification seal” allows the viewers of your blog to verify that the content of the blog post has never been altered since its certification date.

Certify Post

Create strong evidence of intellectual property of your posts and show it to your viewers.

Evan Mattson

This plugin adds information to the admin interface about when each post/page was last modified (including custom post types!).
Enhanced areas:
<ol>
<li>Page/post admin tables – added <code>Last Modified</code> column which is also sortable.</li>
<li>Page/post edit screen (<code>post.php</code>) – added <code>Last modified on: *timestamp*</code> to <code>Publish</code> meta box.</li>
<li>Admin messages after editing a page/post – ie: <code>Post updated. *timestamp* View Post</code>,</li>
</ol>
No options currently available, but the output can be fully customized with filters and the shortcode can be easily customized using attributes!
<h3>Gutenberg, WordPress 5, and Beyond</h3>
This plugin does not yet enhance the new editor provided by Gutenberg and introduced as the default editor in WordPress 5.0. No plans exist to add support for this although it may be added in the future. 
Other areas of wp-admin enhanced by the plugin still work, as does the classic editor.

Last Modified Timestamp

Adds the last modified time to the admin interface as well as a [last-modified] shortcode to use on the front-end.

Certify Post vs Last Modified Timestamp