Funny, I follow a lot of authors on social media and have never seen them use #ad.
"When people refer to their own books in social media posts, these posts are likely to count as ads. This is because they have a commercial interest in selling the book they've referred to.
When Mylene Klass published an Instagram reel that showed images of her book, the ASA investigated complaints that it wasn’t obviously identifiable as an ad (Myleene Klass, 02 November 2022).
Because the video didn’t contain a label that made this clear, and opened with shots of various celebrities answering questions, the ASA ruled that the ad didn’t make this adequately clear."
Will be interesting to see if they do anything about Hunch.