They weren't used to identify a shipper or what was in a particular box, pouch, trunk or something else. They merely sealed a load for security purposes. If the seal were broken the cargo may have been compromised in some way.
The seals themselves were generally made from hard wax, tinned brass, or lead and fastened to the object being shipped. The seals were basically embossed with the pertinent information by several types of machines. They ranged from table mounted models, much like a large heavy duty stapler, to small hand held contraptions that resembled pliers with impressions on both ends of the arms. Others were hammer struck with a striking surface on one end and a die on the other. The smaller sealers often had crosshatched backgrounds which often show on stamped coins. These coins were likely souvenirs struck by workers. The impressions are always weak because sealers were never meant to be used on hard metal objects.
The major manufacturers of the time were the Buffalo Seal & Press Co. and the Keystone Seal & Press Co. in Brooklyn, NY.
Like anything else, they could have and were counterfeited. There are some struck coins that are obvious fakes, but they're likely from modern times.
Bruce
