Which vessel is not required to have a Pollution Placard posted on board?

The requirement for a Pollution Placard on a vessel is typically determined by its size and type of operation. According to regulations, vessels that are 26 feet or longer are generally required to have a Pollution Placard posted on board to inform crew and passengers about pollution prevention measures.

In this case, a 15-foot passenger vessel falls below the 26-foot threshold and is, therefore, not mandated to display a Pollution Placard. This requirement primarily aims to promote awareness and caution regarding pollution, and smaller vessels like the 15-foot passenger vessel do not engage in operations that would significantly raise concerns about pollution in the way larger vessels might.

The other options involve vessels that are all 26 feet or longer, which means they would be subject to the regulations requiring the posting of a Pollution Placard. Therefore, the correct choice highlights that the 15-foot passenger vessel does not need to comply with that particular regulation.