No known IndieWeb Examples.
Starting around 2017-08-25, Twitter introduced "Follow search" as a button and UI prompt to some users.
Stay Informed prompt
When first shown to the user, a UI prompt is provided that explains the feature a bit and provides multiple "Follow search" buttons:
Hashtag follow search UI prompt - from https://twitter.com/hashtag/newbase60
Conditional OR follow search UI prompt - from https://twitter.com/search?f=tweets&vertical=default&q=newbase60%20OR%20newbase64
At some point the UI prompt no longer shows up on search results, leaving only the "Follow search" button near the top - from https://twitter.com/hashtag/indieweb?f=tweets&vertical=default
If you click the "Follow Search" button it is inverted and turns into a "Following search" button:
Hovering over the button turns it red and changes the text to "Unfollow search"
follow search webaction
In a system where different services perform posting, search, and reading services, "Follow Search" would make sense as a webaction that a search service could provide that the user's browser could delegate to their preferred reader service, perhaps on their own site.