It's a pro-police flag. It's supposed to represent the thin blue line between law and order. It's routinely used by people who support the police to a weird extent and as a counter symbol to the Black Lives Matter protests/movement.

It's the "thin blue line" flag, explicit support for the Police State.

It’s difficult to notice due to compression, but it has a blue stripe where one of the white stripes normally is.

https://en.wikipedia.org/wiki/Blue_Lives_Matter