Railroad Blotters

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"... Have you ever noticed when eating at a restaurant the various advertisements found on placemats at your table? This has been one creative way businesses can maximize their advertising dollars. In the 1920s and 1930s, a similar idea was used on something everyone had: ink blotters.
Here was fairly inexpensive way for the railroad to advertise to shippers, as well the general public. Typically about 4 by 8 inches in size, blotters were used to promote freight or passenger service and frequently provided information on specific trains or routes. ..."

Cyberspace World Railroad exhibits Railroad Blotters: Railroads A-F & Railroads G-Z. (The Daily Jive)