I think there's been some sort of unspoken, secret agreement between car designers and automotive engineers where designers get all the celebrity and coffee table books about them, as long as they leave space on the cars to stick badges explaining all the technical stuff the engineers worked so hard for. Maybe there's a backrub exchange as well. That's really the only way to explain the sorts of arcane and frankly, ridiculous badges found on many cars.
This sort of verbose badging about what sort of technology the car contains seems to be falling out of favor a bit, down from a mid-80s era high, when the backs of cars often looked like the window sticker. You could be behind a car and know how many gears it had, whether or not any of those gears were an overdrive, number of camshafts, the manner by which the fuel was introduced into the cylinders, whether it wasn't normally aspirated, intercooler existence, and more. It's sort of like if I wore pants with patches saying things like "Bar Mitzvah'd" and "Dual-Lunged" and "Warm-Blooded" on my ass.
I believe these sorts of informative badges started in the 30s with V8 badging on cars so equipped, and it made sense. That was something to crow about. With the muscle car era came big badges letting everyone know about the engine's displacement, another big marketing tool. It kept on going from there, with the badges being often useful to car geeks, and ignored by everyone else.
The most well-known badge is likely the "turbo" badge, which, in the 1980s, was stuck all over any car to even get near a turbine. "5-Speed" has long been popular, mostly among Japanese makes, who really wanted to let you know about that fifth gear; the more sporting crowd was fond of letting you know that even if you took away one of their camshafts, they'd have another one, usually overhead. Honda's CVCC badge reminded the general public that the Vortexes under that Civic's hood were of the Compound type (you know, for Controlled Combustion), thanks for asking, though almost everyone I knew thought it was Honda's sloppy spelling of "Civic."
While generally most people got as much useful information out of seeing a "DOHC" badge on a car as they would have a "12 VOLT" badge, for some cars, these descriptions were absolutely essential for marketing. Take the "DIESEL" on the back of Diesel Mercedes-Benzes; not only did it remind folks what kind of fuel to stick in there, but it made clear there was a reason why that seemingly new Mercedes was so noisy, smoky, and slow.
The badges almost always referenced some unseen bit of engineering in the car's drivetrain: fuel injection, number of valves, that sort of thing. I always thought this was a bit unfair, as cars are full of little touches throughout, so I've made a few alternative badges in the gallery above to tout some other unsung details. Enjoy, and, feel free to make your own and stick ‘em in the comments! Hell, why not?