Here is a screenshot of what I see of the first few bookmarks I have on Stack Overflow:
Since I have more than 10k reputation on Stack Overflow, I have the ability to see deleted posts including those in bookmarks lists. It turns out that the first question "Why do I get "IndentationError: expected an indented block" in my code" has been deleted, however, there is no way whatsoever to distinguish it from the other bookmarks in either the Bookmarks tab or on the summary page.
Apparently, the same thing happens with followed posts as mentioned in the comments.
Deleted posts used to be indicated with a light red background in the bookmarks and followed posts. Would it be possible to restore this/add a way to clearly indicate when a bookmarked/followed post has been deleted?