CIIIR - Charles III Rex - Royal Cypher.
Perfect. Thank You for Your Service.
This is The One Reliable SVG, that I could find Online.
I have confirmed,
that This is King Charles III's - Official CIIIR Royal Cypher.
Please see These Links to check:
https://www.royal.uk/his-majesty-kings-cypher
https://metro.co.uk/2022/09/26/king-charles-iiis-new-cypher-revealed-as-royal-mourning-ends-17454183/
https://insidegovuk.blog.gov.uk/2024/02/19/updating-gov-uks-crown
https://www.bbc.co.uk/news/uk-63034255