Instruction
One of the most basic and essential uses of signs is to instruct. We see it in our classrooms, businesses, public spaces, and even along the street. Usually, an individual, group, or institution creates them to instruct the public on how to stay in line, therefore dictating their next plan of action. They can also instruct us on any rules and guidelines for consumers. Like FSU uses the "Face Coverings are Expected" posters all across campus. Much like the smoking sign, it's a way for the organization to notify the public about how they must conduct themselves within their establishment. Some are even phrased as pleas so that the staff can adequately execute orderly conduct without mishaps. If guests are requested to do something before resolving their problem, it keeps everything organized, and people rely less on themselves. Instructional signs often act as directional guides to keep us on track and away from being lost or harmed.
As one of the most common uses for signs, instructional signs continue to be the most universal. Countries, rich or poor, use signs to formulate a society that operates in similar ways. There's much to be learned from them.