including a comprehensive safety sweep prior to boarding, and the pilots, mechanics and safety leaders deemed the aircraft entirely safe to fly.”
So they got the same very unprofessional mechanics who wrote on the aircraft to check the tail area?
I'd say it would be mechanics because it's over 20 feet in the air. It's not likely some random person with a big stepladder just happened to be passing by.
first off, the ''artist'' would be easy to find as his or her finger would be dirty...and fingerprints might be easy to find.
Engineers usually have ready access to protective gloves. I'd definitely be wearing gloves if it was that dirty
It would be likely that more than one person would be involved. If they were working on the APU, you would normally need two people to close the APU doors.