Over the next week, expect to hear a lot of booms, pops and crackles as Coloradans celebrate America’s independence.

While fireworks are part of the celebration, they can also trigger fear, nervousness and difficult memories for veterans struggling with PTSD.

“It’s the unexpected fireworks that cause a problem,” said Shawn Gourley, co-founder and executive director of the Indiana-based non-profit, Military with PTSD.

Last year, Military with PTSD started a campaign dubbed “Explosion of Kindness” to teach people about the effects of fireworks on veterans. The non-profit raised money to send thousands of veterans free yard signs that read, “Combat veteran lives here. Please be courteous with fireworks.”

“Coming off of the week of July Fourth, we had over 3,000 veterans on our waiting list waiting for a free sign,” Gourley said.

Gourley said the non-profit shipped 4,372 signs in 2015 all over the country including to Colorado. This year, at least 35 signs were sent to Colorado.

“This is bigger than what any of us ever could have expected,” Gourley said.

The focus of the campaign is not to keep people from celebrating with fireworks, but to encourage people to talk to their veteran neighbors if they plan to set off fireworks before July Fourth.

“Independence Day [is] the celebration of our freedom,” Gourley said. “It’s exactly what [veterans] fought for, and the last thing they’d want is for people to stop celebrating that.”

Gourley said the signs have helped open up a lot of important conversations.

Veterans who’d like to receive a free sign can register here: http://bit.ly/295UKqj

There’s currently a waiting list, but Military with PTSD plans to ship the signs throughout the year.