Free bike, uncomfortable

I found a white Batavus bicycle on the boulevard in front of my house this morning. It's the same type of frame as my single-speed, except in much nicer condition. Other than the missing seat, nothing seems to be wrong with it. All the wires are attached, the pedals turn, the wheels spin. Lots of trash gets tossed into our yard, but why was this bike dumped here? It's a mystery.

As an urban cyclist, I know the rules that apply to abandoned bicycles: you generally leave other peoples' bikes alone, unless they're locked up and neglected over a long period of time, at which point they become eligible for salvage. But what to do about this mostly complete bike that was left unlocked and lying in the grass? In this neighborhood, if I didn't take it, then somebody else would (I have had a small vehicle stolen from this address before). I thought I could keep it safe in my garage and leave a note in case the owner came back for it. If nobody claimed the bike, it would be a good donation for the Bike Depot.

My wife commanded me to leave it where it lies. By tomorrow, it will either have been picked up by the person who left it, or gone to a new home.