Be a good citizen and do a check on bikeindex.org to try to find the owner first, but if you find nothing and the bike interests you, turn it over to the police. Check back in 60 days. You maybe able to become the new owner, according to the police
Don’t feel bad about it. They’re already overwhelmed with them.
If you don’t claim it, then the city will sell them themselves through an auction and keep the money to themselves.