Renowned artist (and communist), Pablo Picasso created a double portrait of the Rosenbergs. As with Léger’s scarves, it was intended to be sold to raise defense funds for the couple and Picasso gave a dedicated copy to the the two Rosenberg boys.

Source: https://espionart.com/2018/06/19/art-in-defence-of-the-rosenbergs/

Musician Paul Robeson rallied and performed for the Rosenbergs
(Source: Robeson, Paul, 1898-1976. Letter from Paul Robeson to W. E. B. Du Bois, January 1953. W. E. B. Du Bois Papers (MS 312). Special Collections and University Archives, University of Massachusetts Amherst Libraries; http://credo.library.umass.edu/view/full/mums312-b161-i267)