This works. And I do it. Too many unhinged people out there. Here in the US, I've found things in restaurants a couple of times and pointed it to the staff.

It clears the liability for all involved, since no one can claim that the staff or a fellow patron 'took it'. It was pointed out by a customer and removed with witnesses. I generally mention it to more than one staff.

I try to baseline assume that the person I'm dealing with in public is not fully there (which would include the property owner). It makes it easier to deal with when it is actually the case.

That's the beginning of a very common confidence game in Europe so I'd probably not do it. But IDK, maybe not in Japan.

Even if you're a local this is the procedure. If the building doesn't have a lost and found (besides the train systems not all places do) then the police box will make you give over your contact information and a bunch of other stuff. It doesn't take an hou (maybe ten minutes if you speak Japanese), but it can be a pain if you just expected to throw it in without any questions.

I happened to study the process few days ago. Officer pulled out an elaborate form, asked the guy if he wants his copy, wants rights to the item if owner didn’t show up, to which he said no and no, and then he was asked to sign the blank and was told him they take care of the rest. Took 5-10 mins max.

Technically no one should ever sign a blank sheet, ever, but that could be done, I guess.