There is a legal term called an "orphaned work" for a copyrighted work that doesn't have a clear owner, or an owner who can't be contacted.
https://en.wikipedia.org/wiki/Orphan_work
Orphaned works are *not* in the public domain. They are still copyrighted, and if the owner of the work should ever resurface, they could technically still enforce their copyright rights at any time. So, anyone who uses an orphaned work is rolling the dice.
Quoted from bluespin:b) The patents on the Stern Electronics company products has long since expired
As Aurich mentioned, patents are completely different. Basically, they cover inventions or methods of doings things.
Copyright covers creations, such as art, music, film, writings, etc.
Anything that is created is automatically copyrighted. However, you can also register a copyright, which makes the rights a bit easier to enforce in court (especially at the federal level) should a dispute arise and be able to potentially collect damages from copyright infringement.
https://en.wikipedia.org/wiki/Copyright_registration
Since when patents and copyrights are mentioned, trademarks usually pop into the conversation as well, but those are something else entirely. Those help enforce the use of a company's name, logo, special product names, special & specific terminology, etc.
Quoted from bluespin:Both Starship Fantasy (Larry) and Pinisder Freeplay40 make ramps
Since you brought up ramps; functional objects cannot be copyrighted, trademarked, or patented. However, the decals (which have artwork on them) are copyrighted. That's sometimes why you see parts created without the decals.