Looking for info on American military padlock

[BBE]

****NOTE****Your key show stamp number that would be cut on your key. If have a letter with four number that would be American Lock code number. They will not give you that code number as they never have as long they been running.....Timothy.....

While his key is stamped with a code, that is not the direct digit code you might normally find on an American Lock key. His has a blind code and that can be determined because the stamped code has a zero in it. American Locks do not have a zero depth.

My understanding of the US Set marking is that it indicates that there is more than one lock keyed alike in a set. This does not indicate MK'ing although the lock may be part of a master keyed system.
BBE.