Roxanne-mail after a US visit?
Say what? Only about 2500km of sea separates Roxanne's home from Singapore...
I don't think the postal office offers such a service. I don't live in the US, but when I sent a package to Japan with signature required, I never received the signature. At the PO I had to stick some kind of card to the package which would be signed and mailed back to me. Never happened. I think that you would have a similar experience.
I guess your best bet is to go with a courier like FedEx or UPS, but that comes at a significant price tag.
If you send something as registered mail then the receiver will most probably have to sign for it, but you will not have tracking information or actually receive the signature. Over here the postal office does offer a traceable service (TNT) but that most probably isn't available in the states and the tracking info is very spotty, anyways.