I have published several pieces about the political street art. For example, see the following articles:

Political street art as a part of 15-M movement in Spain 
Political street art as a tool trying to impact on the society (in Finnish)
Power of Paint: Political Street Art Confronts the Authorities
Paint Like A Girl: Street Interventions Fighting Against Sexual Harassment

At the moment I’m finishing interview-based article about motives of artists that paint political street art.

In addition, please see my Instagram feed for research photos.