JAR-145 old chap.
The company can let anybody sign anything so long as: -
(1) They're authorised by the company exposition / handbook.
(2) The CAA has approved said document.
Within the context of JAR-145 (or JAR-21 or BCAR Section A in a manufacturing company) the individual persons qualifications are only relevant insofar as they form PART of the evidence towards the CAA for approval of the exposition.
G