[ChuckMcM]

All US mail gets a delivery bar code imprinted on it when it is sorted. There are quality checks that verify that the delivery bar code is accurate. Electronic postage is also created using 2D barcodes. My guess is that the folks who build such systems have them just eat bar codes for lunch (which is to say interpret all bar codes) and include that interpretation in the meta data.

If as you say they are never looked at (and I can certainly believe that is true) then the URL you encoded would never be accessed. If however you got a web log entry on your web server that your URL was fetched from a machine run by Booz Hamilton, well there ya go, a bit of information extracted by putting a puzzle in front of them. :-)