In August 2022 the Royal Australian Mint launched a non-circulating commemorative 50c piece commemorating 75 years of the Australian Signals Directorate, with sales beginning in September (https://www.ramint.gov.au/publications/coded-coin-signals-asds-75th-anniversary). The coin's design came with a twist: a secret message was encoded in the coin's design.
The message is not straight-forward to decode: the first hint is on the obverse, with the letters B, T, H, A, S and A in the legend ELIZABETH II AUSTRALIA 2022 each having Braille markings under them. The Braille markings are numbers which give the order to put the letters in, which gives Atbash. Decoding the outside bottom on the reverse (URMWXOZIRGBRM7DRWGSC5WVKGS) with Atbash gives "FIND CLARITY IN 7 WIDTH X 5 DEPTH" and decoding the outside top on the reverse (DVZIVZFWZXRLFHRMXLMXVKGZMWNVGRXFOLFHRMVCVXFGRLM) with Atbash gives "WE ARE AUDACIOUS IN CONCEPT AND METICULOUS IN EXECUTION". The inside text on the reverse (BGOAMVOEIATSIRLNGTTNEOGRERGXNTEAIFCECAIEOALEKFNR5LWEFCHDEEAEEE7NMDRXX5) can be done by arranging the letters into 7x5 grids and reading the columns: it becomes "BELONGING TO A GREAT TEAM STRIVING FOR EXCELLENCE WE MAKE A DIFFERENCE XOR HEX A5D75".
The final answer involves the hexadecimal text on the reverse (E3B8287D4290F7233814D7A47A291DC0F71B2806D1A53B311CC4B97A0E1CC2B93B31068593332F10C6A3352F14D1B27A3514D6F7382F1AD0B0322955D1B83D3801CDB2287D05C0B82A311085A033291D85A3323855D6BC333119D6FB7A3C11C4A72E3C17CCBB33290C85B6343955CCBA3B3A1CCBB62E341ACBF72E3255CAA73F2F14D1B27A341B85A3323855D6BB333055C4A53F3C55C7B22E2A10C0B97A291DC0F73E3413C3BE392819D1F73B331185A3323855CCBA2A3206D6BE3831108B). Using xor with the key A5D75A5D75 gives "FOR 75 YEARS THE AUSTRALIAN SIGNALS DIRECTORATE HAS BROUGHT TOGETHER PEOPLE WITH THE SKILLS, ADAPTABILITY AND IMAGINATION TO OPERATE IN THE SLIM AREA BETWEEN THE DIFFICULT AND THE IMPOSSIBLE."
The Melbourne Mint's output of half sovereigns was sporadic: it struck half sovereigns in 1900 and 1906 for example, but struck no half sovereigns in the intervening five years. A small number of pattern half sovereigns were struck in 1901 however.
In 1980 it was in a list of Melbourne Mint pattern half sovereigns (p55, Skinner, Renniks Australian Coin and Banknote Catalogue, 1980) and it was against listed as a proof only coin in 1985 (p53, Skinner, Renniks Australian Coins and Decimal Banknotes, 1985). In 1989 it was reported that an example was sold for $9,000 in the Spink Australia November 1981 auction (p26, Skinner, Renniks Australian Coin and Banknote Values, 1989).
Two examples were sold as parts of lots 647 and 649 in Sotheby's auction of the Murdoch collection on 21st July 1903. An example was listed and photographed as lot 1015 in a Spink Australia in November 1981.
While Australian half sovereigns had comparatively low mintages, they saw much more use in circulation than sovereigns. In the 1800s the mintages were quite low but through the early 1900s mintages were higher and staying higher.
In 1911 the Sydney Mint struck 252,000 half sovereigns - one of the lower mintages of the decade but the 1911S half sovereign is still a common date. The Sydney Mint was also the only Australian Mint to strike proof half sovereigns in 1911, no doubt to commemorate the coronation of King George V.
Half sovereigns were struck sporadically in Australia in the 1880s and 1890s - both the Sydney Mint and Melbourne Mint struck them in various years but more often than not, no half sovereigns were struck, with the exception of some patterns.
A number of patterns are missing from the Museum Victoria Collection: patterns were struck in most years in the absence of circulating coins but presumably they were for well-connected collectors rather than in a more official capacity. The 1892S half sovereign is one such coin: there is no mention of it in 1980 (p55, Skinner, Renniks Australian Coin and Banknote Catalogue, 1980) or 1989 (p25, Skinner, Renniks Australian Coin and Banknote Values, 1989) but a proof with unknown mintage is listed in 1985 (p52, Skinner, Renniks Australian Coins and Decimal Banknotes, 1985). It is unclear if this is in error but it has gone on to become "Unconfirmed pattern" (p52, McDonald, 2014 Pocket Guide to Australian Coins and Banknotes, 2013).
No circulating half sovereigns were struck anywhere in the British empire in 1888 and very few were struck in 1889. It is believed that their low durability and high production cost prompted the introduction of the double florin as a substitute (p48, Rodgers, Britain's Enigmatic Double Florin in Coin News, July 2020). This explains why the Royal Mint in London produced no half sovereigns in 1888 or 1889. In 1889 half sovereigns were struck for circulation at the Sydney Mint and patterns were struck at the Melbourne Mint: presumably the double florin did not make it to Australia in great numbers, and local demand necessitated a small issue of half sovereigns in 1889. The Melbourne Mint struck perhaps two pattern 1888 half sovereigns.
Early Rennicks catalogues also make mention of the 1888M pattern half sovereign: in 1980 it was listed with the note "Only Pattern Proofs known to exist" (p52, Skinner, Renniks Australian Coin and Banknote Catalogue, 1980) as well as in the list of pattern half sovereigns produced by the Melbourne Mint (p55, Skinner, Renniks Australian Coin and Banknote Catalogue, 1980). In 1985 it was listed as proof only with an unknown mintage (p52, Skinner, Renniks Australian Coins and Decimal Banknotes, 1985). In 1989 it was stated that an example was sold for $9,000 in the Spink Australia November 1981 auction but no other details are given (p25, Skinner, Renniks Australian Coin and Banknote Values, 1989).
Two examples were sold as parts of lots 628 and 629 in Sotheby's auction of the Murdoch collection on 21st July 1903. An example was listed and photographed as lot 1004 in a Spink Australia in November 1981.
In more recent times it has been listed as being of the "Normal IEB" obverse type (p52, McDonald, 2014 Pocket Guide to Australian Coins and Banknotes, 2013) suggesting a recent sighting.