This sounds like something that could be provided as a notary style service. A letter addressed to an individual, only to be handed over on positive ID, care of local business providing this service.

Fun fact: The US Postal Service offers this service, for free. (Though not in an ideal way; they'll just match name to ID, don't uniquely identify an individual. All that would need would be to write a drivers license or such number on the letter too, and the USPS to confirm that.)

when handling substantial matters (big$, felony accusations, etc), I question the definition of "positive ID."