On another meaning of the word bill, I recall reading a joke about a child warning its mother about a bailiff, "Mummy, there's a man at the door with a bill!", She replies (thinking about word for beak), "Don't worry, it's probably a duck with a hat on."
Ha ha! When I was a kid there was a lot of construction work in the city and it all went on behind white painted plywood sheets. Every 20ft or so there was a small sign that read 'Post No Bills.'
I thought the signs were really weird because nowhere could I see a letter slot...