Use Proclaim to add custom slides to your sign feed. If you don’t have Proclaim, you can download it here.
Once Proclaim is installed and open, click File > Open sign feed to see your available feeds.
Select the feed to which you want to add the item, then click Add item. Select the type of item that you want to add and enter whatever information you want and choose a background.
You can also upload your own media for use in your sign feed.