A service advertisement is a prototyping technique that asks a design team to produce a short promotional video, poster, or pitch as if a new service concept had already been launched and was being marketed to real customers. By forcing the team to communicate the service's value proposition as a completed thing rather than a hypothetical one, the exercise quickly exposes whether the concept is genuinely compelling, whether the target audience is clearly defined, and whether the team can articulate what makes the service different in a way that a real person would care about.