Oldie

FISH

Forensic Information System for Handwriting

Might be applicable considering

The USPS uses a program called Mail Imaging, which takes a photograph of the outside of every piece of mail sent in the U.S. While the primary purpose of taking the pictures is to process the mail, law enforcement agencies are able to request images of mail sent and received by a target they are investigating.

https://www.newsweek.com/postal-service-photographs-every-piece-mail-us-shares-agencies-request-it-280614

USSS background info from 2nd pic

https://www.archives.gov/files/records-mgmt/rcs/schedules/departments/department-of-homeland-security/rg-0087/n1-087-06-002_sf115.pdf