Australian, Post Office Seal, Image & Found by Treasure Tib Tibbett.
Found in New South Wales, Australia, ?mm.
Raised circular centre possible marking top right, inscription around border - P.M.(G?) curving downward, AUSTRALIA curving upward // III in sunken centre, inscription around border - ...U..I(R?)W.. curving downward, ...T.. curving upward
From Rhys Hall, PMG = Post Master General. Therefore designated as a Post Office seal.
See Australia Post, "Following federation in 1901, the colonial mail systems were merged into the Postmaster-General's Department (PMG). This body was responsible for telegraph and domestic telephone operations as well as postal mail. An airmail service was introduced in 1914. In 1967, 4-digit postcodes in Australia were introduced, in addition to the world's first mechanical processing centre, which garnered international attention.
On 1 July 1975, separate government commissions were created to undertake the operational responsibilities of the PMG. One of these was the Australian Postal Commission. It later became the Australian Postal Corporation on 1 January 1989 when it was corporatised into what is now known as the Australian Postal Corporation, or Australia Post."