Guerrilla urbanism is pretty much illegal to do everywhere, including in the article's subject city of San Francisco. The goal is to not get caught by authorities while doing it

Society is relatively lenient towards college students being mischievous.

It helps that colleges have their own police forces with a standing directive to not be too harsh on students.

Although maybe that’s a US thing? We are a weird country.

Here in the UK, it seems the best way to get potholes fixed is to paint a penis around it: https://themanc.com/art-and-culture/manchester-graffiti-arti...