Graffiti, which also serves as the plural of graffito, is commonly used as a singular mass noun <graffiti … was depressing people who rode the subways — New Yorker><graffiti comes in various styles — S. K. Oberbeck>. This use is well established although not yet as well established as the mass-noun use of data. Use of graffiti as a singular count noun is still quite rare and is not standard.
Examples of GRAFFITI
The walls of the old building are covered with graffiti.
Form of visual communication, usually illegal, involving the unauthorized marking of public space by an individual or group. Technically the term applies to designs scratched through a layer of paint or plaster, but its meaning has been extended to other markings. Graffiti is widely considered a form of antisocial behaviour performed in order to gain attention or simply for thrills. But it also can be understood as an expressive art form. Derived from the Italian word graffio (scratch), graffiti (incised inscriptions, plural but often used as singular) has a long history. It has been found in ancient Roman ruins, in the remains of the Mayan city of Tikal in Central America, on rocks in Spain dating to the 16th century, and in medieval English churches. During the 20th century, graffiti in the U.S. and Europe was closely associated with gangs. Graffiti was particularly prominent in major urban centres throughout the world; common targets were subways, billboards, and walls. In the 1990s there emerged a new form of graffiti, known as tagging, which entailed the repeated use of a single symbol or series of symbols to mark territory.