People across the internet are calling this "a hardware Easter egg", but it seems more random than anything else. If you buy a Google Pixel or Pixel XL then take out the SIM tray and look very closely, you'll see... Wait, what is that? It's Google's address. To be specific, it's the address of Google's headquarters, though in slightly shortened form. The full thing is 1600 Amphitheatre Parkway, Mountain View, California, 94043, the United States of America. Why would you want to see Google's address every time you put a new SIM card into your Pixel? That's a good question, isn't it?...
Source: http://www.gsmarena.com/google_wrote_its_address_on_the_pixels_sim_trays-news-21231.php
