bbPress Stylish Unread Posts hows a fully-customizable read/unread indicator next to threads (marks topic as read when the user visits it) with a plugin options page.
The plugin options allow easy, detailed configuration of how the indicators display: icon and text, text-only, or icon-only; images or FontAwesome icons; custom or delivered images; etc.
Code output includes unique IDs and classes, allowing for universal theme compatibility as well as extensive customization support via CSS, even beyond the plugin settings.
You can see this plugin in use at https://demo.element-80.com/.
This plugin is also available for purchase at codester.