In Cambridge, Massachusetts, shoppers in Harvard Square are encouraged to write their answer on a Post-it note, then stick it to the storefront of a building under renovation.
As you can see by the video, there's been a large response.
Rebecca Kane thinks it's a great idea.
"I think it just spreads some good positive energy that we can all use in our lives," she said.
Tributes have been left for teachers, parents, mentors -- even Tim Tebow.