I'm not sure a car is the best comparison though.
How about a restaurant putting mint imperials by the cash register. Is it legal for patrons to take one?
Mints are put out explicitly for you to take. Property right intentionally transferred.
Same for any lost property, if you find something valuable (wallet full of cash), you generally have to turn it in to the police, and there is a notification process to try to find the owner, and after a period of time (generally 3 months), if no one has claimed it, it's yours. Again, local laws are going to differ, but the general legal concept, that "A finder of property acquires no rights in mislaid property, is entitled to possession of lost property against everyone except the true owner, and is entitled to keep abandoned property."[1] is common.
There's some old saying about possession being 9/10ths of the law....
[1] https://en.wikipedia.org/wiki/Lost,_mislaid,_and_abandoned_p...
Of someone leaves a car on my drive I can do something about it, you may not be able to do in your territory. I'm surprised there isn't the a legal concept of abandonment though, what do you do if someone drops an empty can on your land?
I'm not sure what all rights (physical or otherwise) might be applicable here.
AFAIK, you can selectively (or not at all) enforce copyright all you want and then change your mind later.
Are you thinking trademark rather that copyright? I'm not sure you can fail to adequately protect a copyright in that sense.
This is not true. Not even remotely true. It is routine that a company notices someone using their copyrights after decades and then sues about it. Oracle is suing Google over code that was "unprotected" for a decade before they decided to sue. In Australia (I know, different country, but this is the same), Men at Work were successfully sued 29 years after they released "Land Downunder" because it has a two bar riff with similarity to a song written in 1928 [1].
As a side note, I see this all the time. What is it about this particular topic that people seem to (a) consistently confuse these things but more importantly (b) feel confident enough about ti to repeat the confused viewpoint with certainty to others?
You are probably thinking of trademarks.