Since flying a pirate flag in open waters would likely attract a "shoot first and ask questions later" response, I was wondering if there is a maritime flag that should be flown when you are using a pirate flag during a film / movie / TV shoot?
The Law of the Sea is a body of case law and treaties, originating from the 17th century book by the legal scholar Hugo de Groot, and generally adhered to by 'civilized' nations throughout the ensuing centuries.
It is now codified in the United Nations Convention on the Law of the Seas, which has International Treaty status, and is ratified by almost all UN member nations, and includes specific tribunals to deal with issues like piracy and actually defines piracy.
Boarding and detaining suspected pirates/vessels under control of pirates is restricted to government vessels.
Where does the Jolly Roger come in? It can still, based on case law, be seen as an intention to commit acts of piracy. However, the Law of the Seas applies on the 'High Seas' and within the territorial waters national legislation takes precedence.
In the absence of any national legislation, though, one could argue that therefore the Law of the Seas applies or can be applied. I don't know about US law, but outside the 3NM zone, on the strength of the Law of the Seas, the US Coast Guard would be entitled to board a yacht that flies the Jolly Roger to ascertain themselves of the real intentions. What happens next is up to litigation lawyers