Mercedes has in Germany, in Sindelfingen, an
AMG factory, which is available to be visited by the public.
Not just any public, though, just a specific type of public, which owns one or more
AMG vehicles.
Quote from
https://www.mercedes-amg.com/en/experience/amg-factorytour.html
"Our individual tours are offered Monday to Friday from 9:00 am to 3:30 pm to owners of current AMG models and members of the AMG Private Lounge. Tours can be arranged via your local Mercedes-AMG dealer."
In the old days, AMG meant having a vehicle engine tuned by the AMG division (same as Brabus).
Nowadays, there are many AMG parts, starting from AMG exterior body kits, to AMG brakes, AMG rims, AMG floor mats, AMG illuminated door sills, etc.
There are also, as you mentioned, people who like to badge up their vehicles, for subjective reasons.
I have recently learned that true AMG vehicles have some distinctive exterior features over vehicles that have only the AMG exterior package, but I personally took over some of those features, and added them to my own vehicle (disclaimer: no AMG badges have been added in the process), making it look more aggressive.
So how do we identify an AMG vehicle?
In my opinion, I like to refer to a vehicle as a true AMG, only (and only) if it has an AMG engine.
There are two options to check this:
- The more obvious one: open the hood, check what's inside
- Check the VIN. The VIN should reflect everything your car has, and what doesn't have (although, adding option codes to the VeDoc seems to be a very easy thing to do nowadays).
VIN codes, however, never change. I can't say about the US VIN, but the EU VIN contains the vehicle model number and type, such as:
(WDD) 172 475
172 is the vehicle model, 475 is the vehicle type, and in this case we are talking about an SLK R172 55 AMG.