My daugher and I decided on the walk to school that the least effective sign of all time was probably a picture of a person at the crosswalk.
The school buses, the blinking crosswalk lights, the looming gradeschool building in the background, the prominent painted crosswalk lines on the street, the crosswalk guard in the fluorescent vest, and the actual, living people crossing the street are already pretty solid social cues for what’s going on.
And people who already don’t regard humans highly enough to slow down when they’re crossing the street under such circumstances won’t be motivated additionally by a picture of a human crossing the street and slowing their progress toward the Really Important Things they’re surely about.
Instead, they should rotate the signs with unexpected images. Like a picture of an eyeball, or a stick-figure hot dog, or a dinosaur. At least people might slow down the first time or two and go, “Wait, did you see that? Was that two guys kung fu fighting on that sign?” It’d have to change fairly often though.
I would accept the paid role of deciding what was on the signs if anybody asked.