On the Overground (or similar metro service), WWYD?
More details - you spotted it after a tradesman of some sort got of the train and it was left where he sat. You picked it up and got off at the next station, and tried to hand it into the desk - but because the person who you suspected it belonged to didn’t get off at that station, they wouldn’t take it. So:
- Keep it
- Hand it into the cops
- Do some social media thing