Certified Candidates (“Certificants”) receive a Certificate ID number and a pdf copy of a Certificate indicating successful completion of the requirements necessary to achieve the Certification indicated on the Certificate. This Certificate may also be downloaded anytime from a Certificant's account on My Portal while Certification is active. (Source)
Linux Foundation certifications are managed, stored in a secure portal, referenced by unique ID, which might mean it can be verified? The portal allow downloads of an official PDF, as well as badges.
Red Hat's certificates are sent by email pdf