The logo of Nine Inch Nails, with a reversed second 'N'. Short form slang popularized by parents and those who didn't realise the letters stood for something. 'Nails' is the appropriate short form.
Nin, or short for Nino is another word for wiener and or the male genitalia oft referred to as the penis. This word was not only popularized but also brought into mainstream culture by Aamir and Uzair, who like E-40 revolutionized an entire culture.