I am trying to research and get an answer for you. Below is a link to a non-Delta site and which is from 2007 and may be helpful. It does refer to a "signing over". If I can find more current info, I will post it. From the Delta T&C, it states that paper vouchers cannot be redeemed online, and that they can only be redeemed at a Delta airport ticket counter or at a Delta ticket office. I know you can transfer ecredits, and I think after reading that you can transfer a voucher, but that might have to be done at either of the same locations I just mentioned above. The use of paper vouchers is also mentioned in the last paragraph of the section entitled Ecredits in the DL link below.
http://en.allexperts.com/q/Air-Trave...el-voucher.htm
http://www.delta.com/planning_reserv...ions/index.jsp