Gender symbol

A gender symbol is a pictogram or glyph used to represent biological sex and gender in biology or medicine, in genealogy, or in the sociological fields of gender politics, LGBT subculture and identity politics.
In his (1767) and (1771), Carl Linnaeus regularly used , and (briefly) (subsequently ) for 'male', 'female' and hybrid plants respectively.
Pictograms used to indicate male and female public toilets became widely used beginning in the 1960s.
Biology and medicine.
The three standard sex symbols are the male symbol and the female symbol , and the hybrid symbol . They were first used to denote the effective sex of plants (i.e. sex of individual in a given crossbreed, since most plants are hermaphroditic) by Carl Linnaeus in 1751. The male and female symbols are still used in scientific publications to indicate the sex of an individual, for example of a patient. In biology, Linnaeus initially used the mercury symbol, , for hybrid but abandoned it in favour of the multiplication sign, , and this is the style used today (for example, "Platanus" × "acerifolia" for the London plane, a natural hybrid of "P. orientalis" (oriental plane) and "P. occidentalis" (American sycamore).) 
Pedigree charts.
Pedigree charts published in scientific papers now more commonly use a square for male and a circle for female.
Origins.
These symbols are derived from the initial letters of the Ancient Greek names of the classical planets Mars, Venus and Mercury and associated with the alchemical elements iron, copper and quicksilver (mercury), respectively. Joseph Justus Scaliger speculated that the male symbol is associated with Mars, god of war because it resembles a shield and spear; and that the female symbol is associated with Venus, goddess of beauty because it resembles a bronze mirror with a handle. Later scholars dismiss this as fanciful, preferring "the conclusion of the French classical scholar Claude de Saumaise (Salmasius, 15881683) that these symbols [...] are derived from contractions in Greek script of the Greek names of the planets".
The use of shapes as gender symbols may have originated from kinship diagrams in anthropology, where a circle represents a female and a triangle represents a male. The earliest form of kinship diagram that displays this is from 1871: Morgan's System of Consanguinity and Affinity of Human Family. W. H. R River's system migrated to big letters for male, small letters for female, while in algebreic-type equations, the numerator denotes male and the denominator female. Later, in C. G. Seligman's 1910 Dance Diagram, outlined circles illustrated females and shaded circles indicated males.
Sociology.
Public toilets.
Gender and/or sex pictograms are frequently used to mark public toilets.
Sexual orientation and gender politics.
Since the 1970s, variations of gender symbols have also been used to express sexual orientation and political ideology.
The first instance of this was the use of two interlocking male symbols to represent male homosexuality.
Since the 2000s, numerous such variants have been introduced in the context of LGBT culture and politics. Some of these symbols have been adopted into Unicode (in the Miscellaneous Symbols block) beginning with version 4.1 (2005).