I started by enlarging a Bat symbol and printing it out (splitting it over two sheets of paper to get it to the size I wanted). Cut out, and trace onto a thin piece of wood:
The jig saw did a surprisingly good job of cutting out the bat shape. I thought I'd have to rough it out with the jig saw and then finish by hand with a coping saw, but the power tool was able to do it all to my satisfaction. I put a hole in the middle for the center of the clock. Then I got a big oval wooden piece from the craft store, found the center, traced the clock body around it, drilled holes in the corner, and used the saw to chop out a space the clock could fit through.
Using a protractor, I marked spots at 30 degree intervals at a set distance around the center of the clock and drilled small holes for later reference. The oval got a coat of yellow paint and the bat shape got black. Added copper nails in the little drilled holes, installed the clock behind the bat piece, then attached that to the oval. The battery can be removed through the hole cut in the center of the oval. This is the finished clock:
And here it is on the wall: