How you know it's time to back slowly towards the exit whilst browsing through the books in a small town jumble sale:
When the first two paperbacks you see are called The Pre-Wrath Rapture of the Church and Winning Your Inner War with Satan. The words 'Armageddon' and 'evil' also appeared to be prominent among the titles on display.
There may, or may not, also have been biographies of each of the four horsemen of the Apocalypse. I don't know. I was backing slowly towards the exit.