FWIW practically all aircraft I have flown have had little scribbled on them - around the fuelling panel, the gear bays or the holds (stuff like "greetings from PMI" or supporting football teams etc). Little bits of innocuous graffiti. Silly prank, nothing more. If someone genuinely had malicious intent they would be most unlikely to advertise it in such a way. Not enough common sense and too much group-think.