If you haven't seen the 2005 "re-birth" of Doctor Who, then this may spoil it for you

The words 'BAD WOLF' appear throughout the series, in episode 2, the Moxx of Balhoon says "This is the classic BAD WOLF scenario"

in episode 3 Gwyneth looks into Rose's mind and sees the big BAD WOLF

in episodes 4 and 5, a kid grafitti's BAD WOLF onto the side of the TARDIS

in episode 6, a helicopter pilots codename is BAD WOLF one

in episode 7, there is a tv channel called BAD WOLF T.V.

in episode 8, there is a music concert poster with BAD WOLF written on it

in episodes 9 and 10, the bomb that is about to hit britain has the german for BAD WOLF written on it

and in episode 11, the Doctor points out that the Blaidd Drwgg project is welsh for BAD WOLF