“The mirror of Venus” ♀ is an astrological and astronomical symbol representing the planet Venus.
In many Romance languages, the word for Friday originates from Latin Veneris dies, i.e. “day of Venus” (divendres, vendredi, venerdì, viernes, vineri); Venus even found her way to Breton and Welsh (Gwener). In Germanic laguages, this day (fredag, Freitag, Friday, vrijdag) became connected with Freyja and/or Frigg, even it is not clear whether they were the same or two different goddesses.
According to Wikipedia, the mediaeval symbol for Venus did not have a horizontal stroke, which was added later to form a Christian cross, while “the idea that the symbol represents the goddess’ hand mirror dates to the 19th century”. In biology, medicine and genealogy, ♀ symbolises the female sex; in sociology and gender politics, the female gender.