Office workers in San Francisco’s CBD have been using Post-it Notes to send messages to people in neighbouring buildings.

More at the SF Gate.

They aren’t the first - The Guardian newspaper reported on the great “Post-it war” of 2011 in Paris:

More at The Guardian:

across the French capital, the summer has been enlivened by a corporate collage contest known as La guerre des Post-it (the Post-it wars). The battle is between presumably underemployed office workers who are devoting large chunks of their days to sticking thousands of pink, yellow, orange and green notes on their windows to recreate pixelated images.