When writing comments it's a common practice to use the @ to address the person you are talking to. Recently, the symbol and the user name after it vanishes after submitting the comment. Is it still visible to the others? How does it work? Thanks.
This was implemented around the beginning of the summer. Both the OP and the respondent will automatically be alerted to your comment, so to eliminate "noise" and save valuable space, any initial "@" reference to either will automatically be elided (and therefore, because it no longer exists, is not visible to anyone). At the same time, SE started to enforce a rule limiting such "@" alerts to at most one other person in a single comment.
I am growing to like the first part of this, because it allows a bit more informality in addressing people who use real names (or at least real-looking names): I can write things like "That's a nice idea, Pablo!" rather than the more formal-looking "@Pablo: nice idea!"