2018 Australia Perth Mint Kangaroo Silver Bullion Series Coin Grades Brilliant Uncirculated. Struck by The Perth Mint from 1oz of 99.99% pure silver in bullion quality, the coin is issued as legal tender under the Australian Currency Act 1965, featuring The Perth Mint’s traditional ‘P’ mintmark.As a Perth Mint first, the coin includes an authentication feature on the reverse. In the form of a micro-laser engraved letter ‘A’ which is within the last A of AUSTRALIAN, it is detectable under a magnifying glass. The authentication feature is designed to make it significantly more difficult for the coin to be counterfeited providing peace of mind to Perth Mint customers.