Very cool. It's good to know that since time immemorial it has always been funny to draw knobs on walls.
Not graffiti , but some Roman , Latin epigraphy... First is a columbarium burial plaque.. C(AIVS) TAFLENIVS C(AII) F(ILIVS) V(IXIT) MENS(ES) VII -( Gaius Taflenius, son of Gaius, lived for seven months) 2nd is a Roman legionary brick of LEGIO SECVNDA AVGVSTA - @ 2nd century.