More often than not with signed for parcels, they fail to deliver by either ringing the doorbell and waiting for 6 seconds before dashing off, or not coming at all. And either way, their system will say "sorry we missed you" and their line will be nobody was available to sign for the parcel. Then their customer service team gaslight you when you complain, because the whole thing is set up to appeal to parcel senders whilst not caring at all about the experience of end-recipients. Your only option as an end recipient is to choose not to do business with companies that deliver via DPD, and to let companies know that is your position.