Q Doodlebug "sign"?

[<hansons@b...>]

Over the holiday weekend, I furnished decals and loaned out my Q 
color pictorial books to a friend who was lettering a brass CB&Q 
doodlebug that he was fortunate to find at an auction for an 
attractive price.
He has mailed me with a question which is:
In the photos, he typically sees what appears to be a sign in the 
rear window. Can anyone tell us what this might be? (A sign? - a 
window shade? - a 'blanked' window for the restroom?)
Thanks for the help.

Roger Hanson
Kansas City, MO.