this feature got dropped in OTRS 2.4 because of the new global overviews (you know you can switch between s/m/l ticket overview mode).
But, I have good news! A much more powerful feature got already implemented for next OTRS major release (OTRS 3.0).
A add some screenshots of this new cool feature to show what I mean.
In future you have the opportunity to see "new message" or also other meta infos on ticket level systemwide. In ticket overviews, dashboard, ticket zoom... and so on. You also will have "filters" to only see tickets in overview with new messages/new articles. :)
Any feedback is welcome! :)
PS: Screenshots are with old GUI (2.x).
-Martin