This is a vintage antique cast iron fencing staple for use with Brinkerhoff's Ribbon wire fencing.  Staples have a bird head appearance and are 2-3/4" in length.  Wire is placed inside of jaws, and driving staple closes jaws.  Knots or eyes on each side were for pulling staple from post (good luck - most will break when pulled especially from the old hedge posts).    Staples have some blackening from fire, probably to reclaim staples from the posts.  Most of this can be removed by buffing.   Staples are in very good used condition.