There are multiple types of watermarks. Standard static watermarks are generally used to ensure content is branded with a logo, and they do very little to deter theft.
Conversely,
dynamic watermarks
dissuade viewers from recording their screen by displaying their email address, IP address, and session ID directly on-screen. Dynamic watermarks also randomly change position, making it very difficult to obscure if any viewer does attempt to record and repost your videos.
Learn more about how dynamic watermarks can improve your video security.