Same here. He called someone and asked him what the symbol meant.

In the version I watched he called somebody and asked what that symbol means.
Lincoln Lee: I lost a partner.
Peter Bishop: I lost a universe!

Nobody told him that was the symbol for a waterfall. He was looking at the map and found it with the legends.

just check a map of the niagara falls
well i just did
the symbol is in fact the one they used in the movie.

So if someone looked on a map and wanted to find a waterfall, would they see that symbol?

Joe was planning to go whitewater rafting, and the man he called was the guide for the trip. There's a scene where they're all sitting around a table and the man is telling them what they'll do at which points. That is also where the maps come from.
Let's just say that God doesn't believe in me.

I don't know, but who was the guy he phoned to ask about the map, who told him it was a waterfall? There's a clue.
"Klaatu barada nikto"

Is it really a U.S. symbol that might be in a park?

Symbol in what way: Chinese character or U.S. symbol that might be in a park?