Isn't it when you pay extra to ensure that whatever the address the delivery item is for,someone has to sign for it. This ensures that if the recipient denied receiving the item the post office can prove that it was delivered? I used to use this when sending off assignments for my Open University courses.
It doesn't offer any extra security, the item can still get lost (as I've experienced), it just means that it must be signed for at the other end. The item just travels along with the regular post. Special delivery, although more expensive, is better as the item is looked after teh whole way through its journey
Apparently the "new" term is Recorded Signed For, which costs 63p more than the normal postage charge. It means that someone has to sign for it on receipt. The maximum amount that can be claimed is �27 if it goes missing. Extra insurance is reasonably cheap and is advised for valuable items. For anything important I would suggest you send goods Special Delivery which can be tracked on line, and have a guaranteed next day delivery with insurance up to �2500. A 500g package with �250 insurance costs �4. Sorry to sound like a Royal Mail ad but I have just had the same discussion with them.
Just a small addition: When you send by Recorded or Special, you get a receipt at the P.O. counter - keep it because it has a consignment number on it. On the same piece of paper is a telephone number which you can call during daytime hours to check on the position regarding delivery. In case of a claim or similar, the same receipt will be essential.