• The @ syntax is intended for notification of a user, so it has somewhat limited temporal utility. Over a longer period of time, it might be that one wishes to identify a Math.SE user by linking to their profile, ie. using the standard [ ]( ) mechanism. For example one might wish to identify the author of a book or paper mentioned by OP as being a frequent contributor here (rather than trying to ping such a user). – hardmath Apr 28 '18 at 17:49