8.6.b requires traceability to the person(s) authorizing the release of product.
8.7.2.d requires documented information that identifies the authority deciding the action in respect of the nonconformity.
How you document traceability is up to the organization.
There is not an AS9100 requirement for traceability of all operators performing work. The use of stamps or initials for traceability to any other persons performing work would be the organization's choice, or a customer requirement.
We have inspection stamps issued to all inspectors, and the person dispositioning nonconforming product has to sign off. We also maintain traceability of weld personnel performing work due to our requirements for continuity to maintain their welder qualifications - this is not an AS9100 requirement, it is a customer requirement.