tagmoji

 Tagmoji  is the use of a single emoji to categorize a piece of content, similar to hashtags, and is supported by at least one IndieWeb site and the micro.blog service.

IndieWeb Examples
The most common form of tagmoji in the IndieWeb is with an emoji in a note.

Aaron Parecki
has supported displaying linked tagmoji on his posts since 2017-02-20
 * example post with tagmoji: https://aaronparecki.com/2017/02/20/7/emoji
 * example tagmoji archive page with posts with that emoji: 🤓
 * links to all emoji used in posts: https://aaronparecki.com/emoji

micro.blog
micro.blog supports tagmoji pages since at least 2021-06-17, instead of hashtags. Examples: Sometimes multiple emoji characters are aggregated into one page:
 * ☕️ coffee https://micro.blog/discover/coffee
 * 📚📖 books: https://micro.blog/discover/books

See also Micro.blog user burk's separate list: https://burk.io/discover/