You only know because you received it. If you were out, or didn't hear the doorbell, you wouldn't know.
Anyone can sign for parcels, it doesn't have to be you. Some services don't even require a signature. Parcels are often left with neighbours, or in a supposedly safe place - in my case, usually behind the plant pot on the doorstep. The theft of parcels from the doorstep is soaring. In the US, "porch pirates" are even following delivery vehicles.
As far as eBay is concerned, it it's recorded as delivered, it's been delivered. No refunds if it's stolen. If you didn't hear the doorbell and your item is sitting on the doorstep, the sooner you're you're alerted to this, the better.
