The Safecracker Arrow was created by Green Arrow a part of his unbelievably diverse Golden Age arsenal. For a time, he created such a broad assortment of arrows that he truly could be ready for any situation. It could be very dangerous if used on a living target, but it is not designed as an offensive weapon.
This arrow is designed to cut through very thick, strong materials. It attaches to to the side of a safe (or a steel door, a heavy lock, etc.) and slowly drills through. Once fired, the arrow automatically continues to work without further guidance from the archer.
This is probably a variant of the Acetylene Arrow, though it might also be a variation of the Drill Arrow.