For PDT and Vaccination Healthcerts, you can check if your results are endorsed by MOH by scanning the QR code provided. If it brings you to verify.gov.sg, and it is issued by MOH (i.e. healthcerts.moh.gov.sg or moh.gov.sg), it is endorsed. There should also be green ticks against the following statements: document has been issued, document has not been tampered, document's issuer has been identified.