Both the empty and
filled circles belong to the oldest ideograms and have been dated to
the period immediately after the emergence of the simplest
conventionalized representations of humans and animals found on the
walls of prehistoric caves and rock faces.
Sometimes is a pictorial sign representing the sun or the moon (see, for example, the prehistoric sign ). The empty circle is often used among primitive peoples to indicate such body openings as the eyes and the mouth. It has been in use in ideographic systems of writing for more than 5,000 years. As an Egyptian hieroglyph was an ideogram for the pupil of the eye.
In astrology represents the human spirit, the inner individual (as opposed to the personality, the outer individual, the individual as he or she is perceived by others). As a symbol for the human spirit is the opposite of matter, , the physical body, and earthly life. Both graphically and semiotically and are almost diametrically opposed.
In Western ideography is a general symbol for the eternal, the endless, that which is without beginning or end, all possibilities (within the confines of the system in which it is used). According to the law of the polarity of meanings of elementary graphs it can also mean nothing, no possibilites at all, as it does as a modern sign for prohibition. The activity prohibited is indicated by pictorial or alphabetical signs inside or outside .
The circle calls attention to those signs it encircles. The signs that are placed within it usually illustrate in what way the endless possibilities of the empty circle are limited. See the international traffic sign as an example.
The empty circle is used in over 50 Western ideographic systems. In astronomy and calendars it indicates the full moon, in meteorology, a clear sky. As a cartographic sign it stands for town, community, center of communication; in electrical contexts it stands for measuring instruments or electric motors. It is used in chemistry to denote the all-important element oxygen without which humans would not survive five minutes. In the old alchemy it was one of the signs for alum. In mechanics means center of rotation. In biology and genealogy it sometimes denotes the female sex (then stands for male).
On modern household appliances such as videotape recorders, it indicates selector for compact disc or selector for TV. On the main switch for electrical power in houses and apartments means power off (as opposed to for power on ).
In several of the systems of hobo signs means here you get nothing, but in the French hobo or gypsy system of signs it can mean both here you must take care, and this is a hospitable house.