agreed. watch the tracking number on the ups site. it will say "out for delivery" on the day that it is coming.
whether or not a signature is required depends on the site you buy from as its an option when shipping an item for extra cost. typically whole computers do require a signature upon receipt.
if you are worried then you could contact ups and ask them to knock on the door or ring your bell when the package is delivered. all of their employees carry cellphones and i think messages come up on their portable scanner as well.
i've personally never had anything stolen when delivered ups... but then again i live in the boonies with a 1000ft driveway