I've made a few projects of this sort for my own use, so I thought it would be useful to have a blank version to quickly make new decoders. Edit the costumes on Sprite1 to add whatever symbols you want to the top of each letter tile. You can also rearrange the tiles in the editor, and save their positions by clicking the message block in the scripts. If you want to add more letters, add to the "letters" list and add new costumes with the letter as their name.