Amnesty.nl are currently protesting the imprisonment of Nasrin Sotoudeh in Iran and Ales Bialiatski in Belarus. Their street guerilla action is to hang images of them, with hands, on all the bars they can find in Amsterdam. That is on gates around peoples houses, parks and train stations. Private property, city property, definitely not Amnesty or a media property. Yes, ad creep is a peeve of mine if it means the city has to clean it up. Inexpensive ingenuity when it comes to media is how Amnesty gets attention since their media budget isn't large.
It's not the first time that Amnesty has used to hand symbolism on public gates / bars though, remember work for idle hands a Badlander back in 2003? That time life-like mannequin hands were used in street grates. And then there was the pretty amazing-looking campaign in London a couple of years ago to highlight the plight of Troy Davis. Still wows me.
Another fun "bar" solution was the one Garbergs in Sweden did, where unlocking your iphone or ipad set the prisoner free.