I found this on Otherthings Flickr page. It a multilayered paint chip taken from a public mural wall that was recently demolished.
This is an extreme closeup scan (2400 dpi) of a paint chip retrieved from the ruins of Belmont Art Park by Amy McKenzie earlier this year. The fragment is about 1cm thick, and appears to consist of about 150-200 layers of paint. (For a sense of scale, note the ridges of my fingerprint in the lower right.) This should give you an idea of the staggering number of pieces painted in this spot over the decades. The park used to be surrounded by one long wall covered with artwork, but that wall was illegally demolished by real estate developers earlier this year.
Streetologist Jan Chipcase explores far flung places for patterns of vernacular street use. His blog is always rewarding. Recently he noticed public charitable donation boxes around the city of Tehran, Iran. Presumably folks put in their loose change.