In the wake of the July 7 attack on Dallas police officers, many have chosen to show their support for the shootings' victims and the police in general by displaying a black and white flag with a blue line near the middle.
The symbol, known as the Thin Blue Line Emblem, has been used by members of law enforcement to represent support for their fellow officers, particularly after police shootings. The symbol reportedly originated in the U.K. with a different flag but is now commonly used in the U.S. and Canada to memorialize fallen officers.
The idea of police as a "Thin Blue Line" between society and anarchy initially entered popular culture in 1988, with the release of a documentary film by the same name directed by Errol Morris, according to Patriot Wood, a woodworking company which began selling Thin Blue Line wooden flags in 2015.
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"To some, that blue line on the flag is just that, but to others, that line is a family crest," posted Twitter user MarT, according to Bearing Arms.
Journalist Katie Pavlich also wore a thin blue line flag pin on "The O'Reilly Factor" to show her support for police officers in Dallas.
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Some interpreters also take the colors of the flag as symbolic, with the black representing fallen police comrades.
The idea behind the thin blue line may go back even further, with Rudyard Kipling's poem "Tommy," according to Patriot Wood. The speaker of the poem calls British soldiers a "thin red line," referring to the color of their uniform, and the typical line formation that they stood in.
"O it's 'Thin red line of 'eroes' when the drums begin to roll," Kipling wrote in the poem, Patriot Wood noted.
Joseph McNamara, a Stanford University research fellow and former San Jose and Kansas City police chief, spoke to the Orange County Register regarding the ideas behind the thin blue line.
"I suppose it sounds a bit corny," McNamara said. "But I have always considered the American police officer to represent the ultimate decentralization of a government of, by and for the people. Cops are public servants with a fundamental duty to protect life and constitutional rights, not an armed force occupying territory."