We have a cast iron decorative salvage piece.  I'm not certain if it is a single curtain bracket holder?  It measures about 3 3/4" in H x about 1 1/4" in W across the widest point.  It is about 1 7/8" in D with both "arms" having a 3/8" across hole towards the front.  It has some light color of red and green with a tad bit of rust. 

Cast Decorative Salvage Piece