Nothing dates a layout like bill boards and the internet is a great place to obtain the picture of photograph you want
I take them and put them into a photo edit program, print the photo and then spray flat lacquer on it to keep it from fading or wrinkle
here is an example of stock photo, and this all by itself is a great simple bill board. copy the thing and build a balsa backboard for it and mount on side of building
this would really liven up and date any layout
who remembers the Coppertone kid?
can even highlight the boards with the miniature lamps most of them were lit up
this might be the most simple yet good looking workup that can be done, and there are tons and tons of old bill boards on the internet, who remembers "Call for Phillip Morris?"
