I think given your situation, the answer would have been easy for me:
Like someone else said, go to the manager (not a teller) and tell him/her the situation, and that you want proof you turned it in.
Now, if I found that envelope say in the middle of nowhere? and with no info on it? I'd thank the good Lord above for keeping
me above water for another few weeks/months and donate a portion of it to a cause I believe in. Only because there's no way
to tell who the owner is.
When I was living in Canadá I found a wallet of a Japanese woman at work so I called the Japanese consulate in Toronto and told them
Her ID was in it, and gave them the romanized name on her credit cards (I can't read Japanese text) and told the contents and our hours.
There was a visa, mc, jcb, and about 30K in JPY ($304.00 USD). I put it in the work safe, and the money/cars/id all stayed there and I assume
it's still there now. It's been about 4 months I'd say.
I have a soft spot for travelers like myself and know how frightening it would be for me. The consulate said they'd contact her, but I guess she
already left perhaps...