Each black arrow is packed with 16,000 LEDs that can display virtually any message: street names, destinations, subway locations, events and more. They can even display news and tweets. Every sign comes with a small keypad where passers-by can select the information they want to see. The menu choices change throughout the day and can include options for "transit," "meals," "shopping" and "sights" — all of it displayed on ever-rotating arrows.