The couple said they contacted the New York police department about the find and said they were told there was no crime attached to the cash and there was no way to identify the original owner of the safe, meaning they were allowed to keep it.
I would only report something with a verifiable ownership. If that safe had an ID in it, you would be damn sure that the rightful owners would get the entirety of their $50,000 and not a penny less.
A hundred k could get you noticed, but then if you're in the US there's significant risk in reporting it to the cops
I'd feel safe handing it to the police here in Australia as we have strong law about lost property, and it certainly would revert to your ownership if no owner could be found