thin blue line

Etymology
By analogy with. “Blue” refers to the color of the uniforms of many police departments.

Noun

 * 1)  The police.
 * 2) A flag or symbol representing the police, commonly associated with the blue lives matter movement.
 * 1) A flag or symbol representing the police, commonly associated with the blue lives matter movement.
 * 1) A flag or symbol representing the police, commonly associated with the blue lives matter movement.