Logos copyrighted?
If a logo consists of mere lettering, even if the lettering is stylized, or if a logo consists of lettering together with common shapes, it is not protected by copyright law.
Surely, neither the Fiat logo nor the Ford logo contain what the US Copyright Office calls "sufficient authorship" to qualify for copyright protection. These logos are just letters and common shapes.
Sometimes a logo does contain enough artistic content to qualify for copyright protection. The Hot Wheels logo is copyrighted, for example. So are a couple of the Tesla logos. American Airlines' newest logo received copyright registration after a nearly two-year court battle. But probably, the majority of logos in the US are not copyrightable.
Logos are trademarked
Fiat 500 and Ford Ka are, however, both protected by trademark law, not just the logos, but the words themselves are protected as trademarks in addition to the logos.
The purpose of trademark law is to identify the source of goods or services. For example, no other car manufacturer but Ford would have the right to put the word "Ka," or the Ka logo, on its vehicles. If it's not made by Ford it can't have a Ka logo.
Trademark law is about preventing confusion among consumers as to the source of goods —and preventing unfair practices between businesses. It's part of a body of law designed to prevent unfair business practices.
So...the question is really about trademark infringement. Would incorporating Fiat's stylized "500" into a stripe on a Fiat car (or two) be trademark infringement? Maybe. Who knows for sure unless you ask Fiat? They would be the one to make that determination. The law puts the responsibility squarely on the shoulders of the trademark owner to determine what constitutes infringement, subject to a final decision by a court. The law also requires trademark owners to police their own trademarks. If they don't do it no one else will. And if a trademark owner chooses to ignore a particular use of one of their marks, then is it not the same as no infringement?
It's for sure that the Ford oval script and the Chevy "bow tie" have been duplicated countless times in all kinds of ways. If Ford and Chevy has chosen to ignore these "infringements," it may be because they don't view them as a threat in any way. And if they don't view them as threats, what will they do about them? Nothing.
Trademark infringement is not a crime in the same sense as, say, murder. When a murder is committed, the criminal must be found and brought to justice to answer for the crime. Whoever pulled the trigger must be held accountable. It's not enough to just stop murdering.
When there is trademark infringement, however, the goal of the trademark owner, generally, is to simply stop the infringement, not to "bring the infringer to justice." And trademark owners usually want to do this the cheapest way possible. A cease-and-desist letter is the weapon of first choice. If a letter stops the infringement, then the goal has been achieved—game over.
And who receives the cease-and-desist letter? If you make a Ford Ka logo that ends up as part of someone's car stripe, who will Ford contact in the unlikely event that they decide to do so? Probably the car owner. The owner will be told, "Take it off." That stops the infringement.
Our sign shop has been involved several times in creating signs with trademarks that the trademark owners claimed were infringements. In each case, it was the sign buyer that was contacted by the trademark owner and told to take down their signs. We were not contacted, even though we made the signs. In fact, we got the jobs to re-do the sign work.
In 2013, when ReMax demanded that a competing real estate company stop using signs that ReMax claimed were trademark infringements, the competing realtor refused and it went to court. The competing realtor lost, and could no longer use the signs, besides ending up with legal expenses. What about the sign shop that made the signs? Were they in trouble for making the signs? No. They were essentially ignored. Except that their work order was used as part of the evidence presented by ReMax against the other realtor. The work order had written on it the words, "use ReMax red and Remax blue." Obviously, no one believed that the sign maker had not acted in good faith.
It was a totally different situation when, several years ago, a screen printer in Kansas City began selling clothing with major league sports trademarks. He was not licensed to do so by the trademark owners and all his inventory was seized and his shop shut down. The NFL, in particular, is very aggressive about policing trademark infringements. And it's no wonder, since sales of NFL merchandise is greater than ticket sales (especially right now).
Similarly, if you were mass producing decals with Ford trademarks and marketing them without obtaining some kind of licensing, Ford might go after you. Obviously, you would not be innocently acting in good faith, and they might do more than just send a cease-and-desist demand. They could go to court to not only obtain an injunction to stop you, but also get all the money you made (times three, usually) of the decal sales.
Brad in Kansas City