The Burbank, Calif.-to-Seattle flight took off and landed without incident on Wednesday, which still doesn't explain Alaska Airlines crews' need to use planes as whiteboards.
"The maintenance team for this Alaska Airlines 737 sure knows how to instill passenger confidence," the Reddit post said. "The method of communication here shows a unique level of professionalism."
Bobbie Egan, a spokeswoman for Alaska Airlines, said the apparent missing chunk was an approved trim repair on the corner flap of the right wing, according to ABC News, and posed no safety threat.
"The small indent shown in the photo was reported multiple times in multiple flight crew reports. A maintenance technician wrote on the wing to acknowledge to flight crews that the repair was made, documented and that the plane was airworthy," she said, adding the message was inappropriate and outside the company's procedures. It was removed shortly after the airline heard about the makeshift graffiti.