Demonstrators were reportedly pepper sprayed and kettled.
Mysterious perpetrators placed the signs on businesses late Tuesday night.
A police officer in St. Louis posted a meme on Facebook, and is under investigation by the department.
The World Jewish Congress says it demanded that Twitter blacklist the hashtag, which recalled the gas chambers used to kill Jews during the Holocaust.
The Smith family's lawyer says the city of St. Louis withheld evidence it had since 2012.
Police Officer Jason Stockley was acquitted today in the shooting death of Anthony Lamar Smith. Newsweek reviewed court documents and broke down the arguments.
Stockley, a police officer, has been acquitted in St. Louis six years after he shot and killed Anthony Lamar Smith.
The police officer is being tried in the murder of Anthony Lamar Smith.