Found a dropped US Passport Card

Hello,

My DB found a US passport card (the new ones for travel to mexico etc) in hammersmith tube tonight.

I'd love to reunite it with it's owner, anyone know what to do?
I could return it to the US embassy (can you call them?) or send it to the police?
Or I could just destroy it?

unsure of best course of action.....

P.S if anyone has any guests and was in hammersmith tonight, tell them to check their wallets!

 Why would anyone who already has a passport (I mean, if they're in the UK, they have to have a passport) pay extra money to get one of those cards?

As I believe passports are technically property of the government, I would return it to the embassy if possible, but I don't think you can go wrong handing it in to the police if that is easier.

I wouldn't destroy it.

Why would anyone who already has a passport (I mean, if they're in the UK, they have to have a passport) pay extra money to get one of those cards?

Perhaps they don't want their passport on them when traveling to Mexico or Canada (not sure why they had it in the UK).  For example, this summer I will be traveling in and out of MN and Canada on canoeing trips.  Having a passport card is by far easier then the actual passport and it is lost, I still have my passport as back up. 

I'd pop it in the post to the US Embassy with a note saying where you found it and when.