In 2003 Ford Australia registered "Territory R5" (TM 982764) and "Territory R3" (TM 982766), and so far they have not seen use.
Although there is a possibility that Ford may use the R6 instead of the XR6 to give XR6-Turbo owners a more exclusive feel. Or maybe the R stands for recreational? Only time will tell.
(thanks to Lisa for the tip).