What do you mean by “traceable”? In the case of cars, virtually all are registered by the local government, and in some cases those records are (I believe) accessible to the public or to others outside the state motor vehicle department.
I’m no expert on gun control, but I believe that in some states they are registered by the government and in others they aren’t. Regardless, in most places there are substantial numbers of illegally owned unregistered guns, which is not the case with cars to any significant extent.
I have no idea about medical implants, but most of the suggestions made in subsequent posts were consumer products that may or may not be registered by their respective manufacturers/vendors. The traceability of such products is not a matter of public record, the way that car or gun records may be.
gotpasswords has pointed out a few cases in which registration of accurate user information with the maker is essentially required: cell phones and satellite TV receivers. However, you can buy pre-paid disposable cell phones that would provide anonymity to a user. In the case of software products, ISTM that in most cases there’s not much stopping one from “registering” with a false name or postal address, thus reducing the potential for traceability.
Also, there are obviously vast numbers of consumer products with serial numbers that are not registered anywhere. Virtually all consumer electronic products (TVs, DVD players, computers, etc.) have serial numbers, but registering them with the manufacturer is voluntary on the part of the purchaser, and I would guess that most people do not bother.
If you want to know who owns car with a specific VIN, or everyone who owns a 2002 blue Honda Accord in Michigan, it’s probably not hard to find that out. Less likely that you could do the same with guns. And far less likely that you could do it with a certain model of TV set.
So what do you mean by traceable: traceable by whom and to what level of detail? What you really want to know?