It started with a simple message - "Hi" - spelled out in yellow Post-it notes on a New York office window.
Then someone in the opposite building decided to respond with a friendly "Sup", also in the sticky notes.
From there it quickly escalated into a Post-it note war between seven rival ad agencies in two opposing Tribeca buildings on Canal Street, with the messages and designs getting more elaborate and ambitious.
"Send Nudez", "Marry Me", "Becky with the good hair" and "If You are reading this, it's too late" are some of the early shots fired in the battle of the stationary supplies, while images included characters from The Simpsons and Dr Seuss, and famous artworks by Keith Karing and Andy Warhol.
The war ended when building management ordered employees to cease and desist, but not before works created a fitting finale - a multi-story mic drop.
Check out the best images from the #CanalNotes Post-it war.