This is the rank insignia for Warrant Officer Candidates in leadership positions while attending Candidate School. The insignia is the same as that used in US Army ROTC. As a point of trivia, taken from the Warrant Officer Candidate School's Standard Operating Procedure:
Candidate Commanding Officer: two diamonds
Candidate Executive Officer: one diamond
Candidate First Sergeant: ROTC First Sergeant insignia
Candidate Class Leader: three discs
Candidate Assistant Class Leader: two discs
Candidate Class Sergeant: ROTC Master Sergeant insignia
Candidate Platoon Leader: one disc
Candidate Platoon Sergeant: ROTC Sergeant First Class insignia
Candidate Squad Leader: ROTC Staff Sergeant insignia
Candidate Assistant Squad Leader: ROTC Sergeant insignia
These insignia are strictly for training and have no bearing on graduation. All candidates are appointed WO1 upon graduation.