From the WIA, original post here.

Date : 02 / 01 / 2017 
Author : Jim Linton – VK3PC

All radio amateurs may substitute their normal VK callsign prefix with the letters AX, on Australia Day – Thursday January 26.  The ACMA automatically allows this privilege which was negotiated by the WIA.

The day commemorates the First Fleet’s arrival in 1788 at Sydney Gove and the establishment of a European settlement at Port Jackson, with the raising of the British flag by Governor Arthur Phillip. On Australia Day many celebrate our country and culture.  This includes the granting of awards, honours and the welcoming to citizenship of many immigrants.  National flags will be flown and the celebrations include fireworks displays.

The AX prefix is popular among prefix hunters and others while the use of a special QSL card is encouraged by the WIA.