Graffito

I love Guy Kawasaki, because everything that he writes is terrific.

Well, almost everything. I recently came across usage in one of his books that made me shudder:

I shot an arrow into the air, and it stuck.
—graffito in Los Angeles

Guy Kawasaki, The Art of the Start 137 (2004).

Graffito is, as Russell Lynes once remarked, a frightfully pretentious word. You should only use it if you want to give the impression of being a literato. Otherwise, use graffiti as both singular and plural, just like normal people do.