Not a direct answer, but related:

I like the idea of modifying billboards so they show subversive messages. This can be done obviously or subtly. For example there was a billboard near me advertising Skye internet as "horror free". I wanted to spraypaint something like "stop selling weapones to turkey, make Syria =>" with an arrow pointing to the words "horror free". But I chickened out and they changed the billboard. I think this term is called culture bombing but that didn't turn up what I was looking for when I searched it. Adbusters had a big campaign around this sort of stuff back in the day.

Peeps in Oakland have also been tearing down billboards and turning them into tiny houses for peeps on the streets: http://narrative.ly/this-graffiti-artist-is-tearing-down-billboards-and-turning-them-into-shelters-for-the-homeless/