The word "海报" is formed by combining the character "海", which evokes the vast, expansive nature of the sea to suggest something widespread or far-reaching, with the character "报", which denotes reporting, informing, or announcing. Together, they conceptually create the meaning of a "poster" or "playbill" as a medium designed to broadcast information broadly to the public, much like how the sea extends widely, ensuring the message reaches a large audience.