On a sunny day in early August, three university students and four children walking near JR Shinagawa Station in Tokyo stopped when they came upon litter on the street.
"Which symbol do you think is appropriate to represent this situation?" asked one of the students from the group, which carried several palm-size wooden cards bearing illustrated icons.
The children quickly flipped through the cards and picked one bearing an eye with a tear. The group then posed for a photo holding the cards in front of them.