A double sided sign with a directional arrow requires a different image to be provided for both sides.

When arrows face the same direction on the frontside file and the backside file (or the same image on both sides), then when they are printed together double sided, the arrows will be pointing in opposite directions.

However, when arrows face in opposite directions on the frontside file and the backside file, then when they are printed together double sided, the arrows will both be pointing the correct direction.