The earliest tattoos found are more than 5,000 years old. In 1991, a 5,300-year-old mummy was discovered in the Alps. He had more than 50 tattoos on various parts of his body, and he is the oldest human ever found to have tattoos. The rationale of tattoos has differed from one culture to another over the centuries. According to history, Egyptians used tattoos to differentiate slaves and peasants. Tattoos spread to China and then to Greece around 2,000 B.C. where they were used as a mode of communication between spies. The word "tattoo" was first brought to the English language after Captain Cook's voyages to Tahiti in 1771. Western sailors then began to adopt tattooing. In the early 19th century, tattooing became very popular with criminals and the working class in Britain and the US; hence the association of tattoos with those belonging to a lower social class. Tattooing retained a negative image until its recent revival as a mainstream symbol of individuality. There are many reasons why people nowadays choose to have a tattoo, and the media is a big influence behind the popularity of tattoos. Tattoos can be seen on people appearing in commercials selling expensive cars. Famous sports heroes and fashion models with tattoos are often seen wearing designer clothes. Tattoos are so linked to ideas of wealth, success, and status that many people would decide to get a tattoo for its fashion and status value. Moreover, some people wear tattoos to express their artistic nature, their beliefs, or their feelings—their individuality. A musician in a rock band may get a tattoo of a guitar on the arm. Some environmentalists may tattoo pictures of endangered animals on their shoulders. Lovers may tattoo each others' names over their heart. A tattoo can be a public sign to show what is important in a person's life. [According to the passage, what function did the tattoos serve in ancient Greece?]