If I wanted that particular shape I'd create an outline, save it to a dxf file, and send that file to my local supplier of aluminum laminates. There they would CNC rout it from either 3mm or 6mm Nudo board. They'd call the next day or so and I'd drop by and pick it up. Your mileage may vary.
The nice thing about doing this way is the outline I send is the outline I get and if I use that very same outline to layout the sign, whatever I end up doing will fit perfectly. Moreover I can cut the outline right along with the image. Then by nipping off the right corners, locating and applying the vinyl is a breeze.