No Exit:

Exit signs have been used to hint at a character’s death before.  I first noticed them in Season 2, In My Time of Dying, hinting at the fact that Dean was between worlds.  His death loomed behind him.  So did it appear behind Dean off and on early in Season 10, after his death and resurrection.  

Now, here they are again, looming behind Sam presaging his sacrifice and imminent death in Season 11.1.