Coins featuring the new King will show him facing to the left. Elizabeth II’s effigy faces to the right. It is a tradition from the 17th century to alternate the way successive monarchs are facing. REX will probably be his Title taken on the new coins.
https://britanniacoincompany.com/blog/prince-charles-british-coin-portraits/ Long waiting for the crown..
No probably about it, REX will be on the British coinage at the very least, replacing REG. It hasn't been on Australian coinage since 1964 so I don't think it will be added now, We'll just have Charles III
The Royal Mint has unveiled the official coin effigy of King Charles III. His portrait will first appear on a £5 coin and 50p, commemorating the life and legacy of the late Queen. The Latin inscription reads ‘King Charles III, by the Grace of God, Defender of the Faith’. https://www.royalmint.com
we're gonna get Charles II on our coins later this year https://www.themandarin.com.au/232045-image-of-king-charles-on-australian-coins-unveiled/ looks like we're getting a different effigy than the Poms this time around, instead of getting the same ones of QEII in the past. the UK ones have the effigy from a sculptor with initials 'MJ' and ours are gonna be from 'DT'