I also made this thing the other night. It is a cardboard cutout painted black and propped up in the window between the shade and the glass. It is soooooo easy, but very effective, don't you think? I'm trying to make all my decorations super cheap and "green" so I used old cardboard boxes that I found in my neighbors recycling. I still have several pieces left, so I think I'll make some giant spiders, a cat on a stack of books, and maybe a dead guy hanging from a noose.
On the subject of being green; I got my costume at thrift stores (charity shops) and have only spent about $15.oo. I'm going to be the Victorian Lady of the Manor. I found $4 shoes, a $2 skirt, a $3 jacket, a $2 hat, and a $2 brooch. I will dress up the jacket with lace at the cuffs and collar, and maybe lots of little jet buttons up the front, and maybe make the shoes more antique looking with fake boot tops and buttons.
So how is your costume coming along?