Just to clarify, there is no "Mint" in Brisbane. The Royal Australian Mint (RAM) is in Canberra. The [ B ] that is incused in the raised square on the coin mentioned here is a Privymark. Info on the coin here.
https://en.numista.com/catalogue/pieces42702.html
There are 7 different privymarks on this NCLT commemorative collector $1 coin but they all originate at the RAM in Canberra. The RAM produces circulating coins and NCLT coins.
There are also 5 Counterstamps on this coin, they are a raised letter on an incused circle such as (A).
There is one other Mint in Australia called the Perth Mint. It only produces NCLT coins, mainly silver and gold. No circulating coins are currently made at the Perth Mint.
Cheers Mike
Master Referee - See my profile for what I collect.