Update 9/20/13 - With the release of the September 2013 Cumulative Update, the icon has reverted back. You can get more information here.
With the release of Security update for Lync 2013: July 2013, there is a change to the icon used for Lync 2013 in the notification area of the taskbar. Instead of the icon showing the current presence state, after applying KB2817465, the icon will now look like the following:
Hovering over the icon will show your current presence state: