What is a distinctive feature of the Marine Corps uniform introduced in 1798?

The distinctive feature of the Marine Corps uniform introduced in 1798 is the quatrefoil. The quatrefoil is a decorative design consisting of four lobes, and it was originally used to signify officers during the early days of the Marine Corps. It was designed to enable identification of the Marines by their fellow officers, particularly during combat situations.

The scarlet trouser stripe, while a recognizable feature of certain uniforms, was not specifically introduced in 1798. Instead, it is a later addition associated with specific ceremonial uniforms. The Mameluke sword is an emblematic weapon presented to Marine officers but was introduced later, in 1825. The NCO sword has historic significance in the Marine Corps, but it also was not a feature introduced in the uniform of 1798. Thus, the quatrefoil stands out as the correct answer due to its unique and historical connection to the Marine Corps uniform from its inception.