Light Up Carnival Sign

Start by spray painting all of your letters one color.
Once the spray paint is dry, tape off the bottom section of each letter and also tape around the outside of the front of each letter as shown. Use your other color of paint to fill in the taped section.
Once that part is dry, remove the tape and use a pen or marker to make diamond shapes emanating from the midpoint of each letter. Use your knife to cut around each of the diamond shapes.
On the back of the letters, you'll want to cut a few holes big enough so you can string your lights through. If your light strands are long enough to go through multiple letters, you'll also want to cut out small sections on the side of each letter so that they match up when put directly next to one another. You can even glue the letters together so that the sides stay flush against one another. Tape the battery packs to the backs of your letters so that the on/off switches are easily accessible.