Commercial Port Operation Areas, especially those that involve military, cruise-line or petroleum facilities.
The Coast Guard, Army Corps of Engineers, and various state entities have implemented numerous restricted areas and security zones around some military installations and commercial facilities in port areas and in other areas, such as near nuclear power plants.
Entry into these restricted areas is prohibited. Violators risk penalties up to $10,000 and could be charged with possible criminal prosecution to include jail time of up to ten years. Even worse, violators may be perceived as a threat, and face a quick, determined and severe response.
If you find yourself unknowingly within a security zone, most likely you will simply be asked to leave the zone immediately, by law enforcement personnel. However, understand that refusal to leave a security zone is considered a serious matter, much like making bomb jokes to airport security screeners, and you will not be treated in a friendly manner.