I'm unsure if I'm to discuss the artist(s) or the piece in the book so I will tackle both.
The Guerrilla Girls are an anonymous group of women who are associated with the artistic society in a myriad of ways; historians, collectors, and even artists. The group is a social justice gathering who spend time and efforts to broadcast advertisements, videos, posters, and more things that are all charged to send political messages. The message they try to send is one of unity throughout the artistic world, promoting equal opportunity for art regardless of the artist's race, gender, or religion. The Guerrilla Girl's movement has been heavily postmodernist, featuring heavy usage of text as well as appropriation of some classical images.
"Do Women have to be Naked to get into the Metropolitan Museum?"
Subject Matter: A classical image of a nude woman, head replaced with that of a Gorilla. Text Reading "Do Women have to be naked to get into the met. museum? Less that 5% of the artists in the modern art sections are women, but 85% of the nudes are female."
Medium: Color Offset lithograph on illustration board (NGA.gov), Poster (Textbook)
Context: The Girl(s) wanted this piece to be displayed in as many public places as it could be. Billboards, train stations, museums, and more.
Meaning: The text gives a great deal of the meaning, that there is a vast gendered divide in what art is shown at the Met. This is a call to action to get more people of color and more women in the galleries. The Gorilla headed woman is an unofficial signature of the artist, "Guerrilla Girls."