It started a few hours after the Battle of New York. The walls of the alleys around Stark Tower slowly started filling up with graffiti. At first it was basic things, Cap's shield, Tony's Iron Man mask. Even eventually a SHIELD logo and, after the official press release, the Avengers A. Tony insisted on the marks all being left on the walls. Though, Clint noticed his support for the graffiti increased greatly after one artist did a particularly amusing depiction of Justin Hammer being squashed beneath one of Iron Man's boots.
Eventually someone labeled it the "Wall of Heroes". People began leaving their own stories. Small things or big about everyday people who had done heroic things. A firefighter who had pulled a boy from a burning building. A nurse who took extra time to make her patients feel at home. A grandfather who had stepped up after the father had left. Normal people doing the things that made the world a better place.
There was an unwritten rule about the Wall. Never erase or destroy or cover up anything that anyone else had done. You could comment, sure, and people /loved/ to comment. There was a ten foot bubble of space around the Justin Hammer piece that was covered in praise for the artist and for Iron Man. This rule was why there were some pieces on the Wall that most people couldn't explain. Usually they were quick little comments, too personal to mean anything to anyone besides the person who did it.
But there was one piece, huge purple letters that no one really understood. Something that Clint hadn't been able to resist adding as the wall had first begun. Two words to remind the world of who the real hero behind the Battle of New York was, even if his deeds were still technically classified as Top Secret. A small monument to the man who he had, at the time, just discovered had survived Loki's attack after all.
Coulson Lives.