9 various sized black frames with glass (Dollar Store)
adhesive backed transparency film for ink jet printers (clear full page labels at Office Depot)
Remove all of the stuff that comes in the frames like pictures of those perfect actor-type kids and the cheap cardboard. Spray paint the frames black if they aren't already that color. Make each letter in a different font. Print them first on copy paper to make sure they fit the frames, then print on the transparency film. Cut out each letter, peel off the backing and place them on the front of the clean glass. Place the glass in the frame, turn it over and put a dab of hot glue at each corner to hold the glass in place. Let cool.
These look best pasted onto the front of the glass, While you can mirror the letters and adhere them to the back, the adhesive shows and distracts from the look.
Don't put hot glue on the frame before adding the glass as it oozes out and shows in the corners.