The content originally appeared on: CNN (CNN Business)Since the start of this year, a series of advertisements have appeared on television screens and billboards across the United States, with ominous warnings to texters. 'I think I left the car unlocked, can you check?' reads a text message displayed on one of the billboards. The consequence, outlined next to the text bubble: 'If your personal texts aren't end-to-end encrypted, it's not private.' In a TV commercial, a mailman hands already-opened letters […]