J. Walter Weatherman
The reason the Bluth kids are obsessive about leaving notes? J. Walter Weatherman, the one-armed man and former Bluth company employee. George Sr. utilized Weatherman as a scare tactic (er, teaching device) when his kids were growing up, as we see through one particular flashback in which George hits Weatherman with a car and his arm pops off. Fake blood spews while Weatherman mutters, "And that's why you always leave a note." As adults, the Bluths are both scared and do the scaring with Weatherman, going so far as to double-crossing George with him in the season three episode "Making a Stand." After Buster loses his hand, he uses Weatherman to teach his family the ultimate lesson: "And that's why you don't use a one-armed person to scare someone."