Simply not true. I took my Classical Archaeology classes back in the mid-70s. The Roman graffiti (best preserved at Pompeii and Herculaneum but also found elsewhere) were discussed at some length.
A notable example is a graffito in a bathroom in Herculaneum . . . "Apollinaris medicus Titi imperatoris hic cacavit bene." . . . "Apollinaris, physician to the Emperor Titus, here s*****d well." Unanswered question during the course: "Was the jolly Dr. Apollinaris caught by the eruption . . . in the latrine?"
Helena at Step 4, Rock 3, Door 5