How can I determine if there's a way I can legally take home a piece of a particular landmark?

Question

Considering to the question of Is it illegal to take a piece of the Berlin Wall, I am interested in knowing what other historical landmarks or sites one can legally and safely take home a piece.

Specifically, how would one determine if an arbitrary landmark has a legal route for acquiring a piece? In the case of the linked question, it was sheer luck that someone who knew a workaround frequents Travel.SE and saw the question.

Consider the avid traveler who might start a personal pebble-sized museum of historical places he had visited. The linked question suggests that he could add the Berlin Wall to his museum. What else could he legally add? The Great Wall of China? The Great Sphinx of Giza?

Answer 1

In order to determine this, one could ask:

1. People with the appropriate authority in local law enforcement (police, etc.) in the jurisdiction in which the monument is located.
2. If it exists, the management of any museum, memorial center or other such organization related to the site.
3. Possibly a local lawyer.

Hopefully, they will tell one to go to a giftshop or something like that. Or they may inform one of something like the special hotel in Berlin.

If one got a yes from all these, then I suppose one could go ahead, but only in the exact manner advised.

If one got a "no" from any one of these, I would advise against doing it.

I want to say that I believe it's extremely unlikely that one is going to find a historic landmark where such people will tell one to go ahead and chip off a piece for oneself. If one is looking for that, one will be wasting one's time the vast majority of the time. It's better to go and enjoy one's holiday than to waste one's time in such pursuits.

Moreover, while I understand that some people might be, I would not personally be interested in chipping off a piece of a monument, even with explicit permission. I believe that the beauty of a monument is in the very location, not in taking pieces away for oneself. However, that's beyond the scope of this question.