For those coming in from google looking for the answer:
UPS Signature Required: first click "Receive Confirmation of Delivery" then on a subsequent screen you'll be allowed to choose what type... and you should choose "Signature Required"
I found this thread after almost doing the *exact* same thing as the original poster. I kept looking, though, because I was thinking to myself, "no, there has to be a positive choice to get a signature, not just a double-negative choice to
not "not get a signature." The checkbox for "Receive Confirmation of Delivery" in no way indicates you'll be allowed to choose the "Signature Required" option later.
At this point, it's obvious to see why many people would assume that
not selecting "Deliver without Signature" would equate to "deliver
with signature." So I can totally understand how they made this mistake and am sympathetic.