The Red Cap of Liberty as told by Art Thompson of the John Birch Society. Edited by Adrian Salsgiver. August 2018.

"What many do not know is that the red liberty caps were symbolic of the male anatomy.” - Art Thompson, The John Birch Society https://www.jbs.org/

The liberty cap was the symbol of freedom and liberty commonly used in the 19th century and is seen in many places in the United States Capitol.
https://www.aoc.gov/blog/liberty-cap-art-us-capitol