If users are unable to sign a logbook due to this showing as greyed out there may be a set status for the signature field.
Follow the steps below to check this:
Click Access Button
then click HR Admin.
Go to Settings then select Logbook.
Click on the specific logbook.
Locate the Signature field and select the pencil icon to the right.
Ensure the field Who can sign has the correct access, this can be set to employee and/ or manager and/ or Admin or can remain blank.