Context: the Thin Blue Line is symbolism for the role of police in maintaining public order. It has been co-opted by the alt-right. There is also a Thin Red Line to represent nurses. The French Wikipedia happened to use it in a legend to explain what the red lines on a map mean.
Me too, but that’s a thin red line in an American flag whereas this is a horizontal red line on a white background. It looks kinda like the English flag with no vertical red line. All I know is firefighters and nurses are pretty cool