Three chevrons, with the points facing down. See related link at the bottom.
On their fatigue uniforms I saw them wearing in Afghanistan and Iraq, there would be a tab at the front of their blouse. The rank insignia would be embroidered on a loop, and this tab would be run through that loop. The actual rank insignia used by the Australians is more the same of those used by the British and other Commonwealth Dominion forces - there may be slight variations (such as the Canadian rank insignia, which has the rank of Master Corporal, and incorporates the Canadian maple leaf into the insignia), but the structure follows the British example, and the crown is an ever present feature on the insignia badges of certain ranks, military unit insignia, etc. (note: this only applies to the actual Commonwealth Dominions/Realms, who acknowledge the British monarch as head of state. Not all countries who are members of the Commonwealth of Nations are Commonwealth Dominions, and the crown is absent from their insignia).
Army sergeant.
There are three ranks within the pay grade of E9 - Sergeant Major, Command Sergeant Major, and Sergeant Major of the Army. There is only one Sergeant Major of the Army.
There is no such rank as Medic Sergeant Major of the Army. There is a Sergeant Major of the Army and regardless of his specialty, it is just SMA.
First Sergeant in both the Army and Marine Corps is E-8.
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The rank of sergeant is denoted by three chevrons on the sleeve of the DPCU uniform (old style) or in the rank-slot on the front of the new design uniform.
The rank of Sargeant has the insignia of three downward-pointing chevrons.
Army uniforms can be purchased from Supply Sergeant, Military Uniform Supply, ACU Army, eBay, Galaxy Army Navy Store, Med-Tech Resource MTR, and US Patriot.
Army sergeant.
There are three ranks within the pay grade of E9 - Sergeant Major, Command Sergeant Major, and Sergeant Major of the Army. There is only one Sergeant Major of the Army.
There is no such rank as Medic Sergeant Major of the Army. There is a Sergeant Major of the Army and regardless of his specialty, it is just SMA.
Sergeant (E-5); Buck Sergeant (nick name).
The first Sergeant Major of the US Army was appointed on July 1, 1966.
Gunnery Sergeant is pay grade E7, and the equivalent Army rank is Sergeant First Class.
No, there is no rank of "Major Sergeant" in the Army Rangers. The ranks in the U.S. Army Rangers follow the same structure as the rest of the Army, including ranks such as Private, Sergeant, Lieutenant, Captain, and Colonel.
Master Sergeant in the Army is pay grade E8. First Sergeant is the other Army E8 rank.
First Sergeant in both the Army and Marine Corps is E-8.