Good keywords and historical moments to Google here are "The Great Northward Migration" and anything related to the founding, population, and history of 19th/20th century Chicago. I believe there was a Chicago newspaper (Tribune, maybe?) that circulated special edition pamphlets to the Deep South with instructions and guidance on how to successfully migrate North. Black supporters caught circulating documents like this could be killed in retaliation -- it was a wild time.

Edit: it was the Chicago Defender.

>Chicago's African-American newspaper, the Chicago Defender, made the city well known to southerners. It sent bundles of papers south on the Illinois Central trains, and African-American Pullman Porters would drop them off in Black towns. "Chicago was the most accessible northern city for African Americans in Mississippi, Louisiana, Texas, and Arkansas." They took the trains north. "Then between 1916 and 1919, 50,000 blacks came to crowd into the burgeoning black belt, to make new demands upon the institutional structure of the South Side."

If a recall correctly, they also circulated imagery and content about the Black experience abroad; for example, in Paris. Arguing that if the condition for Black people was comparatively better abroad, then there was no reason for conditions to remain so dire in the US. This sort of content was particularly enlightening.