A line producer is in charge of organizing the entire show from start to finish. This includes choosing video, writing scripts and ordering all graphics, including boxes and full screens. A sign-off screen is a full screen. The producer decides what she would like the lettering to say and where that lettering should sit on the television. She then chooses the background image or graphic and chooses a color scheme. This all gets written down and sent as a request to the graphic artist.
The graphic artist receives the request and designs the sign-off screen according to the directions given by the producer. She'll be using a system that stores elements as she creates them, so that she can reuse basic screens quickly under deadline. The elements of the screen, including any images and text, are layered, then frozen in place so that a project at any given stage can be taken apart, but, when finalized, will be set completely as a single image.
The artist then sends the sign-off screen back to the producer as a code strip that will be ingested into the server when the show is ready to air. The producer places the code in the show's run-down for the director. The sign-off screen will run as a digital video clip, just like any other pieces of moving imagery. Before digital television took off, many stations used a Chryon system and had technical directors manually typing the full screens into the system before air time.
The sign-off screen sits as coded in the run-down as the show goes to air. With each advancement by the director, the next screen or video prepares to load. The full screens run like video while the over-the-shoulder boxes and lower thirds run in a separate program. When the director takes the final studio shot and hears the anchor begin to sign off, he loads and takes the sign-off screen live, essentially bumping the anchor off the screen, which is why it is referred to as a bump.