I think technically, no one other than the property owner on which bikes had been "abandoned" have any rights to act on them to either dispose or take ownership/possesion after the correct protocols are practiced with the code/law enforcement agencies that deal with abandoned property. I don't think you can be considered a claimant of the property if you are just a person off the street and do not own or control the property the bike was abandoned in.
Anyway, you'd be surprised that many of these bikes are not actually abandoned but just parked by lazy owners who live close by and who would not want to lift a finger to use or move it once in a while. So be careful before you even touch or even get close to many of these bikes, specially in particularly tough neighborhoods. Just not worth the porsible trouble or....pain??
JMOs

Chombi