The signage requires a 1920x1080 resolution. As a result, the preview page will display scrollbars so you can see what it would look like as if you were looking at it on the TV. To see the new preview feature, it's on the left menu under "Preview".
Once in the Signage preview area, you will notice there are scrollbars that allow you to see the entire page. You can change the individual slide with the drop down box. If you have multiple signages, you can change that under the "Select Signage" option.