The UNID for Sandbox is 0xEFFFxxxx. The 5th number determines which modder created that UNID.
Mine is F, so everything I make for sandbox will have the unid 0xEFFFFxxx.
When you post to say you'll help with something, please ask for a specific character.
(Taken from this page http://neurohack.com/transcendence/forums/viewtopic.php?f=5&t=4419 )

Sandbox personal UNID list:
Drako Slyith 0xEFFFFxxx
RPC 0xEFFFExxx