I came across a set of keys on a lanyard. They were

[applegrove]

laying on the sidewalk. I stopped for a few minutes and tried to think of how to keep them safe until the owner could find them. I drew a blank. If I lost my keys I would retrace my steps. An they were off on a sidewalk which is semi busy but not heavy traffic (twenty feet away was much heavier foot traffic). So I decided not to do anything. I asked two people and they said they would do the same thing. As I looked back, there was someone standing over the keys, frozen in thought, just like me. What would you do? Now I wonder if the city itself has a lost & found.

[NYC_SKP]

1. Thought: Post a sign with your phone number, "Found on this spot, a set of keys"?

[hlthe2b]

2. Yes... I'd go with that...

Even if there is a city lost and found, who would ever figure out where it is and and how to contact them...

[Chan790]

3. This is why my keys have a keychain from Tiffany.

It's numbered and offers a reward if they turn them into Tiffany. Tiffany returns them to me. Good Samaritan gets an Andy Jackson for their trouble.

yay!

[Downwinder]

4. You probably did right.

You could give them back to the Officer that was trying to set you up but you might get arrested in route.