Signs have been around forever, at least as late as 753 B.C. in Ancient Rome. They were probably used before Moses.
There are many different types of signs but they are all to communicate. In general, signs may be classified according to the following functions:
Advertisement: they are subliminal messages for the purpose of selling goods.
Information: signs conveying information about services and facilities, such as maps, directories, or instructional signs.
Direction: signs showing the location of services, facilities, functional spaces and key areas, such as sign posts or directional arrows.
Identification: signs indicating services and facilities, such as room names and numbers, restroom signs, or floor designations.
Safety and Regulatory: signs giving warning or safety instructions, such as warning signs, traffic signs, exit signs, or signs conveying rules and regulations.