George Bluth was adamant about his children leaving notes for various things, as to not inconvenience him. He once taught his children a lesson with J. Walter Weatherman about leaving a note when they forgot to leave a note when the milk had run out. ("Pier Pressure")
Throughout the rest of Arrested Development, many notes can be seen in the background. Some are listed here.
The Anonymous hacktivist group left George "Maharis" a note reading "You are about to get screwed like you've never been screwed before. - Anonymous" about Fakeblock. George Michael thought it was from Rebel promising him sex. ("Blockheads")