How to check identity of single signatory in Adobe Sign?

When I want to sign a document just myself, Adobe Sign creates a certificate for the document, but I can't find anywhere in the certificate any way of identifying me. Say I send a signed reference letter for my ex-employee to their future employer. How can the latter check that it was me who signed the pdf, and not my ex-employee that just put my contact details on it and used adobe sign to certify it?