1. If you are adding background images to all your websites, you can add watermark to your images. They are in the image gallery under "Watermarks"
2. If you are making videos to upload to your site, then you can use SimpleVideoPro to watermark your videos. It also has tons of features and you can monetize your videos.
3. You can add watermark to your exported video using Camtasia or any other similar software.