I can confirm that it is ok to operate RC buggies over the massive grassland in JV park , as long as you are not causing nuisance to others and that the buggies are battery operated. There was once I was stopped by the front line C9 staff there, I F them real hard and talked to their park manager, ever since then everything is ok. Some male park staffs even talk to me about RC hobby.
You can ignore the sign which says RC models forbidden. The sign has no where which said "vehicle" or "car". The definition there primarily covers FLYING objects.