Browse through the images in the Trombone History Timeline and you will see that the trombone has had an exceptionally varied symbolism throughout its long history, representing concepts like religion, military, orchestral excess, and musical humor, although anarchic press is one that was new to me. Found this recently and added it to the 19th century timeline (2nd half).

c. 1886—New York: A political cartoon published by Puck magazine targeting the labor movement includes a depiction of an orchestra benefit concert that includes a trombone (which represents the “anarchist press,” as labeled on the instrument). See below image; public domain.