Huge chalk drawings containing messages of peace and hope have appeared on the ground in Trafalgar Square in central London.
Hundreds are adding their signatures ahead of a vigil for the victims of Wednesday's terror attack at Westminster.
The killer, who was shot by police, has been named as 52-year-old Khalid Masood.
People have written "every day be happy" and "we are not afraid".
The drawings are by four artists who have all been homeless for between two months and four years.
Normally they ask for money, but today they are only asking people to contribute their names and words.
They have been handing out chalk.
"We wanted to do something in our own way to stand with the people who died, " Paddy, who's now off the streets, tells Newsbeat.
"We're getting people from all over the world to sign our street art and stand together."
"I started this piece earlier today, but people have now taken it on and added to it," Steve explains.
"I did it as a tribute to the police officer who died to protect us - it's my own little way of paying my respects.
"It's been brilliant to see people from all over the world come and add their messages."
Ben Martin, another one of the artists, says: "Normally Londoners can been quite rude to you.
"Today they've been totally different. Everyone has been really open and friendly to each other. Since I've been homeless, this is the happiest day I've had.
"There have been people of all nationalities adding to it. We've had Turkish writing, and Chinese and French."