FedEx is a shotgun blast. You never know what they are going to do. I think the signature thing is a request made by the shipper, not a FedEx requirement.
I've had FedEx drop HazMat shipments at my back door. I've had then drop them off at someone else's back door. I've had them leave notes. I've had them leave the package with a neighbor. I've had then request a signature.
There is no telling what they will do. UPS is no better.
Once they get the idea of what they are supposed to do, they do a lot better. This is accomplished by calling the shipping supervisors and chewing someone's a%$ out for leaving Hazardous Material where a child can get to it.
Worked for me. I never have trouble with FedEx or UPS now.