This article describes the Persistent Chat options window, where you tell Lync how you want to be notified of new messages in the chat rooms you follow.
Set your alert preferences for new chat room messages
Select the check box(es) on the Persistent Chat options window to choose any or all of these options:
Show the message in a new window (Immediately opens the chat room window where the message was posted.)
Show me an alert (Flashes an alert in your task bar.)
Play this sound (Plays a distinctive sound. Select a sound from the dropdown menu, or browse to a sound file you want to use for this purpose.)
Set your alert preferences for high-priority chat room messages
You can select different or more notification options for messages marked high-priority to help you distinguish them from other messages. Just make different check-box selections to make the alerts for those messages stand out.