Via @MLNow, here's a great neighborhood effort, even with help from a forensic architect, seeking an illegal dumper of construction debris on San Francisco's Bernal Heights.
My added suggestion: if you're trying to find who dropped a bunch of dreck on a public street in an unfrequented part of town, figure out if anyone was camping or living in a vehicle in the neighborhood and ask them if they saw anything helpful. They might really want to help. (Of course, offering a reward wouldn't hurt.) Homeless people tend to resent it when contractors or homeowners dump debris on the street. In part because, when that happens, it's the campers who are likely to get blamed.