Hmmm, IIRC, licenses are not needed for battery operated
helicopters, but i'm not sure about the nitro helis. But, if a
police car rolls by, they won't stop you from playing. They will
just check to see whats happening.
I read an article in which a remote control helicopter pilot was
flying in an open field, when a police car and an ambulance stopped
behind him. It turned out that a person from a distance saw the
helicopter disappear behind a building, and thought that a real
helicopter had crashed, and as such, called the Police and
Ambulance. But this didn't happen it Singapore. IIRC, it was in the
US or Canada.
check out www.daddyhobby.com