This flag is called "Thin Blue Line", which is a pro-police symbol. The origin is from the thought that supposedly the only thing keeping peaceful society insulated from total anarchy is a "thin blue line", or a small number of law enforcement officers who voluntarily put themselves between the two.

However, as noble as the origin sounds, the flag itself is only a modern artistic creation that can trace it's actual creation to the counter-protest of the "Black Lives Matter" movement in support of the police (the ones who were the subject of accusations of racial bias and discrimination against blacks in America) and it often interpreted as a racist dogwhistle, supporting acts of police brutality, extrajudicial killings, and authoritarianism in general.

It's a pretty right-wing affiliated symbol and you see it in conjunction with a lot of other conservative virtue signaling, iconography, and stereotypes.