mister sig'
The company I work for has an ENG procedure documented for the rare case of Capt forgetting to sign the log.
The Operations dept will try to contact both crew members and if possible get them to sign or confirm if any defects should have been entered.
In exceptional cases where no crewmember can be contacted and to avoid significant service disruption, ENG will conduct a review of the aircraft status to enable the aircraft to be released for the next service.
TW