If you were reliant on it? Are you think that method is to public.

You could create your own feed with skyfeed.app using your own specific string of characters instead.

The two emojis that work on their own in regex are: - 📌 & 🔖

I have setup my own feed that searches just my own accounts. Example of the fields needed on skyfeed are: -

Bluesky Post with the above

I have update my own regex to contain the following:-

📌|🔖|ⓘforme:|Note!🔖

So you could possibly use your own keywords for not so public declaration that your bookmarking a post.

My feed in operation, only showing my accounts.