This cute idea and pics come from Hilary Shirley, and she found it via the Tip Junkie.
I bought an 8x 10 shadow box... printed the first letter of the teacher's last name really light in a plain font (I used Century Gothic) and the teacher's name on the side or bottom using a font called Pea Heather's Handwriting. I printed it on cardstock, cut crayons to size with a sharp paring knife and glued on with Elmer's glue. Crayons leave little flakey bits of color, so be careful not to smear your 'masterpiece.' I printed a sample on paper to hold my crayons up to to size them and a cutting board for cutting the crayons on. The cardstock does warp a bit, but it isn't noticeable in the shadow box.