The Drug GMPs explicitly require signatures in the following places:
211.186 master prod & control recs
211.182 Equipment cleaning & use logs
211.188 batch prod & control recs
211.194 laboratory recs (perform & review)
Policy guides and enforcements practices indicate that by interpertation FDA expects signatures on specific records and procedures including any places where company procedures require additional signatures/approvals.
If electronic signatures are used for any of these then since they are signatures required by the predicate rule it is clear Part 11 would also apply for Drug Manufacturers.