It is called a Lozenge.
The lozenge is simply a device to differentiate a First Sergeant from a Master Sergeant, Sergeant Major, etc.
it merely denotes first sergeant status
A diamond.
In the Army and Marines, it's First Sergeant, which are both pay grade E8. In the Air Force, Master Sergeant is pay grade E7, but First Sergeant isn't a separate rank, although it is denoted with a diamond similar to what it used on Army and Marine Corps First Sergeant rank insignia. In the Air Force, the designated First Sergeant can be pay grades E7 through E9.
In the Army and Marines, it's First Sergeant, which are both pay grade E8. In the Air Force, Master Sergeant is pay grade E7, but First Sergeant isn't a separate rank, although it is denoted with a diamond similar to what it used on Army and Marine Corps First Sergeant rank insignia. In the Air Force, the designated First Sergeant can be pay grades E7 through E9.
The Army and Marines both have two ranks in the E8 pay grade - Master Sergeant, and First Sergeant. There is one E8 rank in the Air Force - Chief Master Sergeant. If they hold the position of First Sergeant, they get a diamond on their rank insignia to denote it, but their rank remains Chief Master Sergeant.
A First Sergeant or a Master Sergeant. Which rank they actually are depends on their job. The rank insignias are different. They both have 3 chevrons and 3 rockers, but the First Sergeant has a diamond in the middle and the Master Sergeant has a pair of crossed rifles on the middle. It is improper to address either one of these ranks by shortening the rank names. www.marines.com
There is no such rank as "First Class Sergeant". You have either Sergeant First Class, which is E7, or First Sergeant, which, along with Master Sergeant, is E8.
YES
First sergeant
First Sergeant (E8).
there are two different things and E8 can be in the marine corp. One is a master seargent. It is indicated by 3 stripes up, 3 stripes down ( rockers ) and cross rifles in the middle. Or a first seargent which is indicated by 3 stripes up, 3 stripes down and a diamond in the middle