FAA Regulation

No, the other people in the park are not on notice.  Yes, as long as the park is not busy enough that it would be considered an open-air assembly of human beings.

If the owner is less than 13 years of age. If the owner does not have a valid United States driver’s license. All persons must register their small UA.

ensure that the human beings who are not participating in the operation are under a covered structure or inside a non-moving vehicle. ensure the sUAS is equipped with a parachute make sure the area is closed or restricted-access.

Quadcopter capturing aerial imagery for crop monitoring. UAS used for motion picture filming. Model aircraft for hobby use. 

does not contain any exposed rotating parts that would lacerate human skins upon impact. has an airworthiness certificate issued under Part 21.  is labeled as Category 4.

filed a IFR flight plan. received prior authorization from the controlling agency.  received prior permission from the commanding officer of the nearest military base.

Compliant with Part 107 when used with a first-person view (FPV) camera system. Not compliant with Part 107. Compliant with Part 107.

The aircraft’s Document of Compliance The manufacturer’s Means of Compliance. The Certificate of Aircraft Registration.