WordPress.org

This plugin adds a Visual Subtitle field to all post, page and custom post types that have support for a title.

It allows you to include a string of text that will still be part of the post title, but be wrapped in a span tag, giving something like:

<h1>Visual Subtitle<span class="subtitle"></span></h1>

Keeping it as part of the main level 1 or two heading, means it maintains as much keyword SEO importance as the main title, yet can be given a style (in your own theme) of display: block; to make it visually appear as a subtitle.

The visual subtitle is appended to to the title on on the Posts screen, separated with a pipe (|) character, and appended to the title part of the document title with a colon (:) character.