Back in January, I posted a few 8 1/2 x 11 sheets of signs and posters from various eras here in the REFERENCE forum as PDF files. Here is the link to the original post:
http://largescalecentral.com/forums/topic/20676/signs-and-posters
Here is another sheet for your use. This is a highly compressed image of the sheet.
You can get the uncompressed full 8 1/2 x 11 sheet at:
http://freightsheds.largescalecentral.com/users/bob_hyman/signs/Signs.pdf