Ricardo Delgado designed these signs. He felt that the multicultural population of the station would likely have a wide variety of languages, so shopkeepers on the Promenade might use pictogrammatic signs, rather than written ones. Delgado noted that shopkeepers in medieval times used similar signage, since much of the population could not read. For most of his Promenade signs, Delgado devised a rather abstract style, so it's not entirely clear what they signify. His signs must have worked, however, since most of those shops remained prosperous for the entire seven year run of Star Trek: Deep Space Nine.