Did some background on these a number of years back and I found each individual (rental cars didn't often travel very far from their base back then) region to identify and "mark" cars the way they choose.
As I collected the different methods and styles I started seeing a thread with method and location that often did reflect the regional office the cars (Shelby and non-Shelby Hertz rental cars) were found with.
Dymo tape was popular - both in the typical plastic and the aluminum tapes (each with different stamping devices) for this purpose
Location was dependent on year in general as was the coding. Some were short (not allot of printing) while others were fairly long. Bumpers, door jambs, under hood location and mirrors seem to be the most often used.
Would be interested, Cory thanks for at least providing where the car in the first picture was assigned to - so I can add it to the collection and the spread sheet. Collection is small but more often than not the labels have been removed at some time in the past by owners. Also I would guerss based on what we've seen so far most Hertz regions didn't use this type of identification for the cars. Guessing it was an earlier car?
Did find and purchase an both types of Dymo machines and tapes so that I could help with cars that have been done in the past. Not sure if its worth finding and buying for a single car - especially the metal tape one