Well, this is certainly supercallifragilisticexpialidocious.
The city of Maryborough in Queensland, Australia, birthplace of Mary Poppins author P.L. Travers, have turned on some new crosswalk lights. These pedestrian lights feature the silhouettes of the magical nanny, umbrella and all: Umbrella up/green light = "Cross with care," and Umbrella down/red light = "Do not cross."
Where I live “Don’t start crossing, but finish crossing if you’ve already started” is represented by the red symbol flashing (as opposed to staying lit continuously for “Don’t cross.”) In this case I suggest instead using a yellow umbrella flying around like some sort of arrow. Even better would be if that symbol were accompanied by some sort of whistling noise, to assist vision-impaired pedestrians.