According to americans living in the cities, what was a sign of a communist revolution in the untied states

Union activity--During the early 20th century in cities, unions were tied to communism. 

Communism involved a revolution of workers. Due to the tactics used by unions, such as bombings, strikes, and riots, people saw unions as the means to a worker revolt. This gave unions a bad reputation until the 1930s when Franklin Roosevelt began to recognize the rights of the worker.