I've been noticing some random signs around the city, labeling and commenting on construction materials. At first, I thought they were a form of street art and were connected. But after discovering this blog, Enough with the plywood and this article on the matter, it's clear that the first sign is an isolated work by some North Beach activists who are unhappy with the site of the boarded up building.
The second one is interesting ... and actually very political, referencing both a controversial chemical used in warfare — most recently used by Israel (though they were US-made shells) —and the "Angel of Death", Josef Mengele. The Nazi physician has recently been in the news in regard to the speculation that he is responsible for the unnatural concentration of twins that has occurred in the community of CÂNDIDO GODÓI, Brazil.
It took a bit of internet digging, but I found some more info about this second sign on Tales of the Freeway Blogger (an activist who places signs about the war on freeways around the country). Visit the site for more pictures and to read more.