The 4th -17th -19th Light Horse Regiment

The Prince of Wales’s plumes and coronet supported by two horses above a boomerang inscribed ‘Prince of Wales’s Light Horse’.
This example in silver plate. To the reverse two loops N-S.

Regiment formed 1948, badge approved 1949.

References:
Festberg, Alfred N. Australian Army Insignia 1903-1966 (Amazon UK link)