Vincent van Gogh, Cafe Terrace at Night, 1888
This is a bridge in Paris. You hang locks on it with the name of you & your boyfriend/girlfriend/best-friend then throw the key into the river. So even though the friend/relationship may end, you can’t remove the lock. It stays there forever, as relevance to someone once a part of your life.
National Geographic, 1972. Young lovers in Paris by Gordon W. Gahan.