Weird query, the only thing I ever have to sign for is phones. I get a lot of online crap delivered to my house. There must be some reason that phones are singled out.
I usually have to sign for expensive electronic goods, anything that's around $500 or more in value. Depends on what you order, certain items would need to be signed for as well. Might also be the policy of whoever the shipper was (FedEx or UPS etc).