WWI era hallmarked, engraved silver and gold decorative fob named to Corporal H. McK

World War One era hallmarked, engraved silver and gold decorative fob named to Corporal H. McK who served with the Australian Imperial Force (A.I.F.).
It is in a diamond shape and has four points like arrowheads with two smaller arrowheads between each - the area between them being circular. One side has tarnished over time. There are engraved lines from the centre extending to the arrow points and a central shield made from gold which has the text 'H. McK Cpl' engraved into it.
The reverse has the 'STG' mark on the left arrow point and several hallmarks on the lower arrow point. The central are is lightly engraved with what appears to read 'A.I.F. / Days Service / 1st Reinf.'
Despite the fob itself being pforessionally produced, the added engraving and decoration is more amateurish, making it difficult to interpret.