I asked for permission at a large federal park and was told that recent policy has been handed down that it is not allowed- across the board.
Now, since I did ask very respectfully, I was informed by the HMFIC Ranger that if I happened to know anyone who owned adjacent property, well, then there really wasn't anything he could, or would do if I launched from there. (can you say fpv?)
With that said, I think I have been seen launching from on park property, and since I stayed clear of all people and any potential issues, and I keep as low a profile as possible considering the novelty of the thing, I have no issues yet.
I can guarantee you if somebody complains, or if there should be a malfunction and a crash even remotely close to a person, or if it were to cause even the slightest damage to a monument or attraction, or even the trees and shrubs, then I am sure all bets are off.
I am hyper diligent to not be that guy who gets plastered all over the internet with a Phantom doing something stupic and then carrying the blame when we are all grounded.