Lync CU2 introduced the Lync Meeting Tab or what I liked to called the PizzaWheel because the icon looked a lot like a pie or pizza. This gave you the ability to access Lync Meetings directly from the client.
This morning my computer running Office 2013 Click-to-Run updated Office in the background and I noticed that the pizza wheel is no longer and has been replaced by a more traditional calendar icon.
In order for the meeting icon to be changed you need to ensure that both CU3/November patch is installed along with KB2837643 which includes the image dll files needed. I suspect we will have issues again like we did with CU2 where people will not see the icon at all if this patch isn’t installed.