My gas station guy saw it, and seemed embarrassed to tell me, but eventually did, that some wrote “bad thing on my car”. I got out to look. I thought it was written in my “dust”, but when I went to wipe it off with the rag he gave me, I realized it was a permanent marker.
He removed it with gasoline.
The rear of automobiles has always been called the "rear deck."
Even in rear-engined cars.