While scrolling through the special features, there is a billboard in the background. If you highlight it and press your Enter button, you will access and interview with Steve Martin on his inspiration to use the billboard to give the main character "signs".
There are some interviews with the cast available in the Biographies. A couple of symbols (such as a musical note) will appear, and if selected will access the interviews.
All easter eggs were generously submitted by SirDonk