Show tickets as Read / Unread, like email does
Similar to the way all email apps work: unread emails are BOLD and as soon as you read it it goes UN-bold. It is a quick visual way to know if you have missed something.
The idea would be to use some kind of indication of when a user has a ticket that they have not yet read, or, a ticket that has been updated and they have not yet read the update. Could be bolding, or background colour, or font colour, or just an icon.
The tricky part is that tickets are not static like emails are. You may read a ticket, and then a minute later someone else makes an update. The email would have to turn bold (unread) again because you have not read the update. Programmatically it's basically tracking the read status of each ticket at the user level. And when the ticket gets updated the read status is reset.
We do have a "unanswered" queue, that, basically, lists all tickets that require attention.