Lewis, former treasurer of the Service Employees International Union, has collected more than 4,200 posters from around the world through various organizations and conferences, from friends and through the Internet, according to a city press statement.
"The collection includes various themes and serves as a way to communicate ideas and convey a message," reads the statement. "This particular exhibition encourages diversity and focuses on embracing differences and promoting tolerance."
Lewis has displayed parts of his collection in Massachusetts public libraries and two State Heritage parks, the statement adds. For more information, email Stephen Lewis at email@example.com.