The word "丁丁" is formed by reduplicating the single character "丁", a pictograph originally depicting a nail. This repetition creates an onomatopoeic term that mimics the sound of clinking or jingling, such as metal striking metal, as used in classical Chinese contexts.
Word Definition - 丁丁
dīng dīngTintin, cartoon character; (neologism) (slang) penis (丁丁 resembles "JJ", which is short for 雞雞|鸡鸡[jījī]); sound of chopping wood, chess pieces hitting the board etc