What insignia denotes an E-4 in the Marine Corps?

In the Marine Corps, the insignia for an E-4 rank is indeed represented by two chevrons up with crossed rifles. This designation specifically refers to the rank of Corporal, which is the fourth enlisted rank in the Marine Corps. The crossed rifles symbolize the Marine Corps’ focus on marksmanship and combat readiness, highlighting the skills expected of a Corporal in terms of leadership and proficiency with their weaponry.

The other options represent different ranks or insignia. For instance, two chevrons alone typically denote a rank lower than E-4, while three chevrons with a rocker represent the rank of Sergeant, which is E-5. One chevron up with crossed rifles would indicate the rank of private first class, which is E-2. Therefore, the insignia of two chevrons up with crossed rifles specifically identifies the E-4 rank of Corporal, making it the correct answer.