I believe that you have been looking for help regarding ISO 17025 requirements.
17025 says this about what they are looking for on a calibration certificate in section 7.8.2.1:
o) identification of the person(s) authorizing the report;
A lot of labs also attempt to meet the older ANSI Z540 requirement, which is slightly different:
- a signature and title, or an equivalent identification of the person(s) accepting responsibility for the content of the certificate or report (however produced),
The person is often the quality manager, but it is whoever is the person delegated the authority to determine that the calibration results being presented are correct and meet requirements.
Many labs also include the person performing the calibration as one of the persons responsible for the content of the results.
If you want to add more, there is no reason why you cannot. I have sen a few labs that have their certificates notarized! However, I would counsel against adding extra signatures - extra stuff can come back to bite you in a audit.