Signs inspired by the billboards in the film have been used in protests by numerous groups around the world. Both McDonagh and McDormand have responded positively to this, with McDonagh saying that "You couldn't ask for anything more than for an angry film to be adopted by protests,"[49][50] and McDormand saying she is "thrilled that activists all over the world have been inspired by the set decoration of the three billboards in Martin's film."[51]
- On February 3, 2018, a mural was erected outside Bristol city centre in England depicting three billboards like those in the film, which read: " Our NHS is dying", " And still no more funding", " How come, Mrs May". It was installed by the groups People's Republic of Stokes Croft and Protect Our NHS in response to the alleged privatization of the National Health Service (NHS) and the death of a 15-year-old girl that the coroner attributed to neglect caused by a lack of NHS resources and care.[52]
- On February 15, 2018, Justice4Grenfell, an advocacy group created in response to the Grenfell Tower fire, hired three vans with electronic screens to protest perceived inaction in response to the fire the previous June.[53] The vans were driven around London and displayed messages in the style of the billboards in the film: " 71 Dead", " And Still No Arrests?", " How Come?".[54]
- On the night of February 15, 2018, the movement #OccupyJustice set up three billboards and a number of banners in Malta to mark the four-month anniversary of the murder of journalist Daphne Caruana Galizia. The billboards bore the text: " A Journalist Killed. No Justice.", " A Country Robbed. No Justice.", " No Resignations. No Justice.".[55][56] The authorities removed the billboards the following day,[57] stating that they were illegal.[58] The government was criticized for this move,[59][60] and a day after their removal, activists laid down banners with similar text near Auberge de Castille, the office of the Prime Minister.[58]
- In response to the Stoneman Douglas High School shooting that took place on February 14, 2018, in Parkland, Florida, activist group Avaaz had three vans circle Florida senator Marco Rubio's offices displaying: " Slaughtered in School", " And Still No Gun Control?", " How Come, Marco Rubio?".[61][62]
- On February 22, 2018, the Union of Medical Care and Relief Organizations, protesting the inaction of the UN in response to the Syrian Civil War, set up three billboards outside the United Nations building in New York that read: " 500,000 Dead in Syria", " And still no action?", " How come, Security Council".[63][64]
- Shortly before the 90th Academy Awards ceremony (on or around March 1, 2018), conservative street artist Sabo set up three billboards in Los Angeles, stating: " We all knew and still no arrests", " And the Oscar for Biggest Pedophile goes to...", " Name names on stage or shut the hell up!"[65]
- On International Women's Day 2018 (March 8), three billboards were put in downtown Pristina, Kosovo, to protest the death of two women as a result of domestic violence.[66]
- On March 24, 2018, signs inspired by Three Billboards appeared at March for Our Lives gun control rallies across the U.S. and around the world.[67][68]
- In January 2019, Chinese artist Wu Qiong and a gay policeman launched a public protest campaign in which bright-red trucks bearing slogans denouncing homosexual "conversion therapy" were paraded through several major cities in China, including Shanghai, Beijing, and Nanjing.[69]
Wang Qishan, China's vice-president, said he understood supporters of U.S. president Donald Trump, in part, through watching the film.[70]
