Initialism of yen or initialism of yuan. The two lines represent the other two letters in the word 'yen'. One of the earliest uses of ¥ can be found in J. Twizell Wawn’s “Japanese Municipal Government With an Account of the Administration of the City of Kobe”, published in 1899. Usage of the sign increased in the early 20th century, primarily in Western English-speaking countries, but has also become commonly used in Japan as well.
– cifrão
