Seen on the train in Melbourne, Australia. They could have said “passengers” instead of “passenger.” The sign would have worked just fine that way, while avoiding the awkwardness of the verb-subject disagreement. But I don’t really mind. We don’t have a good way to say he-or-she, so I’m ok with “they.”
I do present heorshe (and hisorhers and himorher) to the world. They would be difficult to spell as well as easily mispronounced. I say we go with it.