Victor Mair has a Log post going into great detail about the many uses of the symbol Q in Chinese. I had been familiar with it only from the title of Lu Xun‘s famous “The True Story of Ah Q” (阿Q正傳), but it has many other uses:
If anyone should try to outlaw Q from all Chinese writing, then there would be no way to talk about the most famous work of modern Chinese fiction or the best-selling Chinese mini-car, and one would not be able to describe the texture of mochi, gummy bears, and lots of other delectables, nor would one be able to ask one’s friend to Q him on QQ, and you’d never be able to get out of Warcraft II.
And it is used for a basic Cantonese swear word: “the Q is read as [lan2] (‘vulgar morphosyllable for male sex organ’). Since lan2 does not sound at all like Q, the Q is not being used for phonetic purposes, but may perhaps be graphically suggestive.”