The word graffiti is a plural noun in Italian. In English graffiti is far more common than the singular form graffito. There is no substitute for the singular use of graffiti when the word is used as a mass noun to refer to inscriptions in general or to the related social phenomenon. In such contexts, the use of Graffiti as a singular is justified by both utility and widespread precedent. In English Graffiti is a singular noun in much the same way data is. It is a popular form of the word “graffito” in English.”]
Source: https://gizmodo.com/wii-spray-wiimote-hack-breaks-up-the-family-fun-with-a-5014389