Where a signature has been offered at the point of booking, but not selected, that carrier reverses the right to 'leave safe' without the requirement of a signature.
Where a signature has not been offered, that carrier will only provide a 'signed for' service, unless otherwise requested in transit, by the recipient.
If the courier is unable to deliver the goods, due to no one being at the delivery address, no neighbour to leave with, or no safe place, that courier may redirect your parcel to the closest ParcelShop location, to ensure both a quicker and (mostly) more convenient delivery.
LEAVE SAFE: Leave safe deliveries should be out of the sight of  the general public (those people that would not have a reason to be passing such as; residents or workers of the building, that the goods have been delivered to), i.e. which is not an exposed doorstep from public view.
Where non signed for services are requested, unfortunately the carrier provides no liability for loss.