I. grə-ˈfē-(ˌ)tē, gra-, grä- transitive verb
( -tied ; -ti·ing -(ˌ)tē-iŋ ; also -ting -ˈfē-tiŋ)
Date: 1964
: to draw graffiti on : to deface with graffiti
graffiti ed walls
II. noun
Etymology: Italian, plural of graffito
Date: 1945
: usually unauthorized writing or drawing on a public surface
Usage:
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.