 According to Matt Groening (qv), viewers were able to decipher the  alien language that is sometimes seen in the background the same  night as the pilot episode aired. The only primer for the code in  that episode was a sign that read "Drink Slurm". The sign appeared  once with the word "Drink" written in the alien code and once in  plain English. This resulted in the producers creating a second,  more complex alien code to be seen in the background of later  episodes.