They got the Gold "A"

In February 1916, Brigadier General John Gellibrand, commander of the 6th Brigade, had suggested that the veterans of Gallipoli's Anzac Cove should wear some distinguishing mark.
He proposed an embroidered gold "A" to be stitched to the colour patch. The practice originated in the 2nd Division, and in 1918 it was widespread.
By then, the great majority of the 120,000 AIF men serving on the Western Front had not been at Anzac, and the golden "A" was a proud and relatively rare mark of service. It was an indication of the importance the AIF attached to its veterans. Apart from the Anzac insignia, other symbols marked out the veteran. On the left sleeve he wore a chevron for every year of service; red for 1914 and blue for each subsequent year. Even more important was the gilt chevron which indicated a battle wound.
Some men - not all of them veterans by years of service - wore four and five such chevrons. A very few wore six.
The groups of reinforcements which reached the battalions from training camps regarded the hardened warriors with great respect.
Cpl. Ivor Williams, my father, wore two chevrons but due to the only photo I have is black and white, it was taken in 1917 in London. I am unable to determine the colours. One thing I do know is that he was over there 4 years and was wounded at least twice.

Read the full History of the 21st Battalion written by Captain A. R. Macneil, M.C. (One who was there)