The only time I take unattended things, such as a bike, is if it is in a dumpster or in the street pickup pile. Even then, I ask the person at the residence if it's OK. Now, I picked up a bike out of a curbside trash pickup pile once, it was a pretty beatup steal rigid Raleigh MTB from what looked like the early 90's. The frame was still great, but everything else except the handlebars, derailleurs and wheels needed to be replaced (BB bearings were rusted solid). The owner of the residence said he didn't want it anymore. I built it up with spare parts for a kid in the projects of Dallas who wanted to curb hop with his buddies.