I would take it in and my mom would probably take care of it while we try to locate its guardians/contact the state. If I was living alone I would do the same thing.
Crying babies make me lose my mind, up in here, up in here.
Why are people saying they would wait for the child's guardian to return? Would you really give the baby back to the person who abandoned it? Even if the parent/guardian did change their mind and return, I wouldn't give the child back to them. If they're abandoning their baby then they aren't the sort of people who should be taking care of it in the first place.