I could be wrong here but that’s a squeal device whereby it’ll make a riot of a sound when pad material is low by rubbing on the disc.
I guess they expect you to replace all four together (which is logical cos they should all wear at the same rate)
I think it needs to be fitted so that when the pad wears down and that “tang” touches the disc, the direction of the disc pushes the tang away from the pad not towards it.