I think it's important how much you consider a wad to be...but if it is substantial, this is what I would do....create a new web address through yahoo or google or whatever. JUST FOR THIS, so you can cancel it after. I would put an ad in the paper...lost and found...just say money found on train platform...email this address:________________ with amount and which train platform and I will contact you if I did find your money. I'd run it twice and then if no correct responses, hey, it's yours...finders keepers. You don't have to donate it, ya know....
It's Christmas time, I don't think it would be too unusual for people to be carrying around large amounts of cash to buy gifts with.