I had posted this last year as an unknown. This piece having come in a small group of British and Commonwealth signs. While searching for an unrelated item I came across the accompanying 2d photo. It appears this sign was worn on both shoulders of this RAAF uniform.
Photocredit. Rathbone Museum of WW2 Aviation. A wonderful site.
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"We must make our mistakes quickly"
Major General George Alan Vasey CB, CBE, DSO and Bar
New Guinea 1942