It's to remind people of the great tragedy that took place here, so they won't ever forget that a peaceful village of Indians was wiped out by the conquistadores back in the 17th century.
11 seconds sound clip from the The Leopard Man (1943) movie soundboard.
You can hear this line at 00:57:49.592 in the Blu-ray version of the movie.
Quote context
[...]
- But I've got something to tell you that will change all that.
- It wasn't an animal. It was a man.
- I don't know, and I need your help to find out.
- Oh, Mr. Galbraith. I'm so glad you're here.
- Oh, that's very interesting.
- Well, now that you've had your history lesson, I think I'll get on to the museum.
(castanet clicking in crescendo)
[...]