In general, you can choose the name of a double-faced card's back face, such as Awoken Horror (C.R. 201.3d, 201.3). If you choose the name Awoken Horror with Runed Halo, then the protection granted to you by Runed Halo would, among other things, prevent damage that sources named Awoken Horror would deal to you (C.R. 702.16e).
EDIT: Correctness edit after comment 3 was posted.